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Your Email Can’t Be Sent? Let’s Fix it Ourselves

January 19, 2023 Sarvar 0 Comments

You’ve just finished an important project or concluded several lucrative deals. So, it’s time to go home and to relax watching TV with a cup of tea, but first you decided to send some bulk emails to your partners, notifying them of your success. You press the “Send” button, dreaming about soft armchair and… “Ding!” says your PC and there is a problem – your email can’t be sent.

A familiar situation, isn’t it? However, you don’t have to call Technical Support ASAP. Let me tell you about typical problems you may face when your email can’t be sent and about their possible solutions.

Only a lazy bugger does not use E-mail today. We use it for personal needs, business correspondence, for newsletters and email marketing – sending e-mails is now natural for us, as well as eating toasts for breakfast. However, a toaster will never show us strange error messages, while e-mail tries to trip us up frequently.

So what can prevent the e-mail delivery? There are five most typical problems, which can arise when you are sending e-mails. Especially if you are sending bulk mail and if you are using your own SMTP server:

  • Sending to incorrect e-mail address
  • Wrong email-client settings
  • Firewall or anti-virus that are configured incorrectly
  • Problems with ISP and block-lists
  • Wrong DNS configuration

Incorrect e-mail address

A problem, that often arises. It happens, when we are trying to send e-mails:

  • With large attachments
  • To the wrong recipient address
  • To stale recipients (abandoned accounts) or
  • To accounts over quota.

Always check e-mail address and attachments size – don’t forget, that most servers do not support attachments, larger than 10Mb and non alpha-numeric e-mail addresses (like car*l/ So, your email can’t be sent (they may be detected as spam or rejected.

It is a very good idea to check and prune your mailing list especially if you are doing mass mail periodically. Remove any email, that didn’t deliver 3 times in a row. Most mass mailing software on the market will provide this option automatically.

It is in your best interest to keep your mailing list as lean and fit as possible, because most Internet providers you send email to will count the number of errors you get with your recipients. If you have an unhealthy list, you will get lots of errors and rejections. In such cases, your provider might block you completely, because they will suspect you are sending spam.

If your list is well maintained, there will definitely be some errors with it, but the amount of errors compared to amount of correct emails will be very low and your provider will pass it without problem.

Improperly configured e-mail client or SMTP-server software

This can create bigger problems – almost unnoticeable errors during configuration will prevent sending e-mails and you will spend hours searching for proper tips. To avoid such “email can’t send” situations you should verify that the POP (or IMAP) and SMTP server (for outgoing mail) are configured correctly. Host and port must be exactly specified and your user-name and password must be spelled out correctly. You must literally check it letter to letter observing capital and small case letters.

Firewalls and Anti-viruses

The next problem you could face – our brave firewalls and anti-viruses. They struggle with undesirable actions and programs, most of the time, they will also block the programs we need. If there is a problem with your outgoing mail, verify there is no firewall software blocking email traffic on port 25, 465, or 587 (those are the typical ports for your outgoing email).

Check your built in Windows Firewall, as well as any other firewall software. Pay particular attention to all those modern anti-virus “suits”, most of the time they might contain not just your standard anti-virus, but also another firewall or internet filtering software.

Those are quite paranoid, blocking everything left, right and center. Check if you are affected by a firewall built into your Internet sharing router. Although less frequently, this still occurs.

If you have all three of them, you might consider switching off the software firewalls and leaving the one on your router, because if you have each packet of your incoming and outgoing traffic examined and scrutinized by 3 different firewalls, it will severely impede your speed.

Your Internet Provider

Another widespread problem you can have when mass mailing – your ISP (or Internet Service Provider). Many Internet Providers block port 25 intentionally, just to prevent you from spamming.

If port 25 is blocked, you will get a response message such as “Connection refused” or “Connection timed out”, and it is impossible for you to run your own SMTP server to email. If that happens, give your ISP a call to find out the real reason of the problem and ask them to open port 25. Please, note that some ISPs give you only web-based email accounts and disallow using SMTP protocol to access their servers at all. Consider switching to a competitor ISP (there is definitely no shortage of decent providers, that are cheap and will not block you on every step).

Block Lists

Finally, let’s talk about block-lists. Block-list is a database of IP addresses that indulge in spamming.

If you are running your own, local SMTP server, you will have a real problem if your IP address is blocked by one or more of those block-lists – as a result your email can’t be sent. Each list has it’s own criteria on why your IP may end up there, but fortunately, there are services on the Internet, for example, that allow you to check if your IP is blocked or not.

Some programs, such as Email Delivery Server, conduct these tests as well.

So, if your IP will end up in a block-list it will cause you problems with sending mails.

This is especially true if you have a dynamic IP.


Because every time you connect to the Internet, you get a different IP, so often times you will get a new dynamic IP, that is blocked by the block-lists and you’ll have no ability to email.

Get a static IP. Just ask your Internet Provider, most of them will be happy to allocate a static IP (free of charge or for some small monthly payment). Getting a static IP will make running your own SMTP server much easier.

It is also very useful to verify your IP on the block-lists. If your IP is blocked you should do everything possible to remove it. Most block lists contain detailed instructions on how to remove your IP address from their list.

DNS entries for your domain name

If you are running your own SMTP server, you need to remember about direct and reverse resolution for your domain.

If you still do not have your own domain name, get one now, they are so cheap ($10 a year or less), there is no reason why you would not have a decent host name.

Let us consider this example: your IP address is and your domain looks like “”. (Of course, in your case, name and IP will be different).

Make sure that your provider has added this to their DNS:

  • “ A” (host name resolves to IP
  • “ PTR”. (IP resolves back to host name, which is also important for SMTP servers).

These records describe the relation between a host name and the corresponding IP address in DNS.

Here is a short checklist:

  • Check your mailing list as often as you can – remove all stale and not working emails
  • Be sure, that you customize your e-mail client or SMTP server email software correctly, check every parameter and make sure it’s exactly right
  • Disable blocking of outgoing traffic in your firewall. Check if you have more than one firewall.

If you run your own SMTP server, also check:

  • Verify your ISP doesn’t block port 25
  • Don’t forget about IP block lists and check your IP from time to time, or if you see any problems delivering your messages. Sometimes your IP could be added by mistake
  • Check your host name for forward and reverse DNS resolution
  • Don’t spam;)

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