A list of SMTP and IMAP servers of popular ISPs

Frequently asked questions (FAQ)

In short, no, you will not be blocked by your Internet Service Provider (ISP). This is because our entire software is web-based. All you would be doing is uploading your mailing list through our control panel. Every part of our email validation process from there is run from our online email address validation software. We process it for you and in this process, neither your computer nor your IP address is involved.

Quite fast! Our system scales from just a few hundred email addresses waiting to be cleaned to millions of email addresses. So whether you are verifying 2-3 email addresses or millions of email addresses, you can be assured it will be completed within a reasonable amount of time. It comes with great support from our amazing team, software features you’ll love and our innovative list cleaning process.

No. We never send any emails to anyone in your contact list. The way we find our whether an email address is valid or not is using email simulation technique which does not involve sending any emails.

No. There is no software installation required to use our service. All you need is a web browser (Chrome, Firefox, Internet Explorer), which almost every computer in the world has. Simply drag and drop your mailing list and the process begins. Our staff will take care of the rest and let you know when your mailing list is ready to be downloaded.

In very simple terms, our email verifier works by simulating the email sending process with email receiving servers. We disconnect just before the actual email sending process and we get validation of whether a user exists or not by doing this. We have two sub-processes - pre-validation and post-validation. Each process prepares your mailing list for the next stage. Currently, your list is validated against 12 different stages and they include things like deduplication, domain check, spam traps, complainers check, risk check, syntax check, MTA check, suppressed email validation, unbalanced delimiter check, mailbox error check, custom TLD removal, and EV scoring.


Once you finish creating an account, you will be asked to verify your email. After verification, you can log in to the control panel and top up your account. Then launch an email validation job from there. It’s as simple as that. Our control panel is made to accommodate even the most novices of users.

Once you login to our control panel, click on “Validate Email” button. This will let you drag and drop your mailing list that you would like us to process. Once uploaded, your job begins and you will be informed once it’s ready to be downloaded. You can go back to your dashboard and watch the progress of cleaning happening in real-time.

We currently export the file in CSV format regardless of which format you supply to us in. You can give us a TXT or CSV file to work with and we do the rest.

Any data you have in your CSV file besides the email address field will stay intact. When we take an email address for validation, we take the data in that row alongside it. So whether it comes out as valid or invalid, the row data will continue to go along with it, and therefore everything stays intact.

We would say, we are up to 98% accuracy. We derived that number after validating millions of email addresses and then taking sample data to send actual emails to. Our innovative technology allows us to accurately validate each email by directly getting in touch with the customer’s mailing server. Whether you are verifying private emails (Eg. @company.com) or ESP service provider’s email (Eg. @gmail.com), you can be assured that our system is just as good. We have developed relationships with these major ESPs to provide you with amazingly accurate results.

Not really, we can validate just about any email address. We can even validate other country’s email addresses without issues. We are not limited to the just United States. We can verify ANY email address in the world. Every time our system is unable to determine its validity, we automatically have it registered for our developers to have a deeper look at. We will get in touch with the customer who have uploaded the list and let them know that we weren’t able to validate some of the email addresses they have on the list and then our developers will provide them with a verified list once we have a fix. Alternatively, we simply refund their money for the inconvenience caused.

We have a large spam trap email addresses database that uses AI to derive highly accurate indicators which we then use to check every email against.

For lists, which exceed the 10,000 contacts mark, we suggest verifying them every 2 weeks. Smaller lists can get away with monthly check-ups. This is because email addresses are often changing and from statistics available, we can say users continually change their email addresses and providers for that matter. Sending invalid emails will not only render no results but also put your reputation on the line. A higher bounce rate would mean lower deliverability rates and worst - rejection of all emails coming from your server or address.

Absolutely! Just get in touch with us through email or launching a ticket through our control panel and our staff can assist your needs.

Security was our top priority when designing our application. From the time you start browsing our website to the time you launch jobs, everything is secured and sealed. We use powerful encryption (same as the banks) and we take all measures to protect our customer’s data. We are also HIPAA compliant, which adds to the benefits of using our email validation platform.

Yes! Please check out our email validation API page for more details on how to use it.

Yes! If you are planning to validate anything over 3 million emails, get in touch with us and we can arrange a special price for you.

Yes! Once you sign up, you will get free email credits to test our service and our API. Enjoy!

‘Unknown’ status means the email could be valid or invalid but more so invalid than valid.  It just means that we used all our processing techniques to try and validate that email address provided to us but we don’t have sufficient evidence (50-50) to say if it’s valid or invalid.  In general, we highly recommend sticking with the ones we stated with certainty that they are valid to avoid an unnecessary spike in bounce rate. You can get rid of the unknown status easily by sorting it out through CSV. Our suggestion is to submit unknowns from time to time so we can validate them again for you. Generally, over time, things change, and sometimes ESPs allow validation of those IDs that they didn’t allow previously. This could reduce them further.

We suggest you to get in touch with us. The support center FAQ section is to assist with the majority of the commonly asked questions when using our service. It’s not meant to answer them all. Our friendly staff would love to help you further with your enquiries.

Yes, we currently restrict it to either a CSV or a TXT file. We suggest using CSV not just because it’s more compatible across all operating systems but also because it can contain data beside each email row (Eg. First Name, Last Name, Phone, and so on…).

The companies range from multinationals like BMW and 3M Group to smaller local businesses. We serve all types of customers in all kinds of industries. As time passes by, their mailing list is prone to invalid emails as well and they use us to get rid of them so their email campaigns and marketing efforts render a higher return on investment (ROI). We hope you would use us too. We are sure you will benefit from greater customer reach and eventually improvement to your bottom line.

It just remains in your account until you want to use it again!

We often get a question asking why you see ‘unknown’ status listed next to an email address that has been validated. While the causes differ from time to time, here are a couple of answers that would explain further and hopefully help you have a better understanding of the results we provide our customers.

What are ‘unknown’ status codes?
‘Unknown’ is one of the outcomes that our software generates as a result of it falling outside the categories of valid, invalid, undeliverable, unreachable, disposable, and others. When our software concludes an email address as being “unknown”, it would mean that we tried every single trick under our sleeve to validate that email address. Some of these tricks include verifying the syntax, domain checks, MTA checks, and many others. You can see more about what is checked on our email validation process page. After thorough checking, we were unable to conclude that the email address is valid or invalid or whether it’s deliverable or not.

When do we put ‘unknown’ next to an email address?
The most common reason for putting this status code is when the mail server that we are trying to connect to doesn’t reply with a yes or no. When we validate email addresses, mail servers usually reject mail if the user is not known or doesn’t exist. It also throws out a whole lot of other errors for other reasons like Mailbox being full and so on. So when the mail server doesn’t respond with a definite yes or no, we tend to report back similarly. We mark it as ‘unknown’.

How can you identify an email address as being ‘unknown’?
Most of these mail servers don’t respond because they only give you the status of the email address AFTER you finish sending the message. This means we have to send a message to your recipient before we get a bounce message. For us, it defies the purpose of using our service since you could easily send a message yourself and figure out whether it exists or not.

What other types of events can cause the ‘unknown’ status?
Another common reason a result is marked as being ‘Unknown’ is when it times out. We have a timeout in place which gives up on a connection if it is not responding for a certain amount of time. This happens more so during API interactions than direct upload. After a couple of tries, if it’s still timing out, we mark the email address with the status as ‘unknown’. In simple terms, we want to talk to the mail server but the mail server is not talking back to us so we say, that’s ok, that we will come back later to say Hi again.

How many ‘unknowns’ will there likely be on my list?
It is really hard to predict a number as each list has varying domains and email addresses. For B2B lists, we observed a rate of anywhere from 10% up to 60% and 15%-25% being the average. Most of the email addresses that are US-based tend to say “Hi” relatively fast and respond with status on whether an email address exists or not. The issue is with International Mail Service Providers who don’t like talking a lot.

In conclusion, the best way to put it in terms of ‘unknown’ status is being neither good nor bad. It’s not something to avoid sending to but neither should you have 100% confidence that it won’t bounce. Our suggestion is to split the unknowns into a separate file and include them with a greater number of valid. That way, over time you will know easily which ones are valid and which ones are bounces. This will also help you keep your reputation up as a sender.

Another suggestion is to submit ‘unknowns’ over time so our system can validate them again. Sometimes, ESPs allow validation of those IPs later in time than they once didn’t allow. This could reduce the number of unknowns in your list and help you in achieving better deliverability.

Yes, we do! Please get in touch with our team to get our company bank details. Once received, your credit will be added to your account on the very same day. We understand that some companies prefer to make large payments via bank transfers but do note that we cannot predict the time it would take for your funds to reach us. We ask for your patience as the banks get busy clearing the funds.  We supply this service as part of our commitment to keeping our customers happy.

We get asked a lot about how the results file looks like. This article will try to explain just that. Right after your email validation job is complete, you will receive three files - valid, invalid, and unknown.

The valid file contains all email addresses we believe to be valid and working. The invalid file contains invalid email addresses that have negatively responded to our validation requests and the unknown file usually contains all the ACCEPT-ALL (where the mail server accepts any email that is sent to it and processes everything later) or email addresses that we couldn’t determine the validity for.

Valid - A valid email address has been verified as a real email that is currently accepting mail. SAFE – These emails exist and have been verified for safe sending.

Invalid - An invalid email address has been verified as a bad recipient address that does not exist or is not accepting mail. Invalid emails will result in a bounce. DON’T SEND – These emails do not exist and are not safe for sending.

Catch-all - This is also known as an “accept all”. This is a domain-wide setting where all emails on this domain will be reported as a catch-all. There is no definitive way to determine whether this email is valid or invalid. SAFE – If you have a dedicated email server with your own IPs, catch-all emails may be safe for sending dependent on the overall health of your list. DON’T SEND – If you use a third-party email provider that requires a bounce rate below 4%, these emails are not safe for sending.

Unknown - We are unable to definitively determine this email’s status. This email appears to be OK, however, the domain and/or server is not responding to our requests. This may be due to an issue with their internal network or expired domain names. SAFE – If you have a dedicated email server with your own IPs, unknown emails are normally safe for sending. DON’T SEND – If you use a third-party email provider that requires a bounce rate below 4%, these emails are not safe for sending.

Role and service-oriented emails - also known as role-based emails are usually assigned to a group of people. In other words, they are assigned to people managing a specific role within a company (Eg. CEO, Marketing, Customer Service). They do not belong to a specific person which makes it a risky email to send to.

Our customers use this option to avoid sending email campaigns to the ones they are less likely to get a response back from. Worst-case scenarios include the users of that email marketing your email campaign as spam or unsolicited email which degrades your reputation and decreases your email deliverability. Some examples of role-based emails include admin, customer, contact, marketing, and so on.

Bad address - Detection of spam traps or complainer email address - Bad Addresses are a combination of a lot of things we watch for. We have a massive database of spam traps and complainers’ email addresses. These addresses have been carefully sourced from the most reliable sources, and they provide us with live updates on what is most likely a spam-trap or a complainer.

Sending to spam-trap is the worst nightmare for an email marketer. They are risking their domain, reputation, IP address, and more. In addition to this, we also have a trained artificial system that recognizes what emails are likely to be spam-trap or of bad quality. We help you eliminate sending to bad addresses.

Free address - Free Email Service Providers, when selected, allows our system to identify if the email address that was entered or uploaded to our system belongs to one of the free email service providers. There are a lot of free email service providers like Gmail, Hotmail, and Yahoo.

Our email validation software can accurately identify less popular ones as well as the most popular services. We mark them as “True” which means the email address in question does belong to a free email service provider or false. Some of our customers choose to exclude sending to free email addresses because most of them can be used by spammers to create fake emails. Sending emails to these addresses would profit you nothing.

Disposable address - Disposal Email Addressing (DEA) refers to providers who supply disposal email addresses to their customers. This helps people protect their real email addresses from getting abused with spammy content. It’s good for the customers who are making use of these services but not so good for email marketers who want to reach them.

Each disposal email address provided has specific time frames for shutting down a particular email address. We have a database of hundreds of domains that supply these disposable addresses. We help you avoid sending to these addresses and thereby increase your response rates from sent emails.

Did you mean? - Typo Suggest is also known as a typo correction feature offered by many applications like Microsoft Word and other such utilities. They figure out if you’ve typed something by mistake and offer you suggestions on possibly correct words. Similarly, our software examines the email address you have entered or uploaded.

It will then, looks for popular email address providers around the world to see if it matches any of those. If it does, it will come up with what a correct email ID should look like. A good example might be an email address that looks something like this – “[email protected]”. This email looks to be correct but it’s very closely associated with one of the most famous email service providers – “yahoo.com”.

EV Score - is our internally developed algorithm that tells you the quality of an email address by assigning it a value from 0 to 1. After scanning through millions of email addresses and seeing their deliverability, we can accurately assign quality scores to email addresses that you are highly likely to get a response back from.

We help you increase your ROI by allowing you to decide on sending to leads that are highly likely to open and click your email campaign. A higher EV score indicates a good quality email address while a lower score might potentially have higher spam or bounce rate issues. We recommend sending to lower EV with caution. The value itself is anywhere between 0 and 1.

We have been in this email communications industry for a very long time (10 years to be precise and counting). We know and understand the importance of email and how it affects businesses. We have cleaned millions of email addresses and each job improves our system for the next. Here are some other reasons why people prefer us over our competitors!

1) Accurate email address validation
2) Validate email addresses in bulk or via API
3) Innovative 12 Stage cleaning process
4) Easy and secure download and upload of email data
5) Typo correction and syntax fix up
6) Top-notch security and reliability
7) Friendly staff and best support

Email marketing in generally considered to be one of the best direct marketing in the world. Its return on investment (ROI) is something to boast about. You only spend a little to achieve big results. To be successful, one of the most crucial steps is having a list free from spam traps, complainers, and invalid email addresses. This is where the Spotzee email validation comes into the picture. Our software cleans up invalid emails and other non-working emails from your mailing list. We are here to make you a successful email marketer. Upload your email list to us and watch our software go to work.

Whether you have new mailing lists or validating your old ones, you are bound to have email addresses that are likely to bounce or are invalid. Most email marketers say their list is double opt-in but you would be surprised how many of those kinds of customers come to us and realize their mailing list was actually more “dirtier” than they thought. With that said, there is no such thing as 100% clean list either. Email accounts get activated and deactivated over a period of time and you can never have a 100% clean email list but who said you can’t try for at least 98%, which is what we offer.

Considering you are a seasoned email marketer, you know the cost involved in sending email marketing campaigns. The preparation involved and the effort put into it to render results. Most of the time, many end up spending 1000’s of dollars sending to dead or invalid email addresses. That means all that effort is likely to bring little or no reward since ESPs don’t like you (owing to your bounce rate) and you only reached a very few active customers on your mailing list.

We help you get rid of old, invalid, non-existent email addresses that are likely to generate a lot of bounces and cause your ESPs a lot of grief. Spotzee’s innovative email validation process intelligently cleans each email address at an astonishing speed. Our system scans and verifies each email’s existence within milliseconds whilst scanning it against millions of spam trap and complainer records we have in place.

There are also hundreds of rules and validation algorithms in place to give you that accurate validation result you are after. This in turn gives you an email marketing campaign you can boast about with ROI your boss would be pleased with. Your email marketing efforts will not go to waste using our service.