ISPmail Stretch

Prevent spoofing with DKIM

Email sender spoofing is the act of pretending to be in control of someone else’s email address. This is a common problem with phishing. Frequently scammers send emails with a sender address of something@paypal.com and hope that the recipient falls for it and trusts them. In fact SMTP does not care which sender address you …

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Fighting brute force attacks

So many bad guys everywhere. Paranoia you say? Well, take a look at your mail log. While I was preparing this guide I could barely follow it. The mail server I used for testing was by far not ready and I already got visits by a bunch of chinese IP addresses trying to guess accounts …

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Success stories

I would appreciate if you leave a comment here telling others if your mail server is running. Perhaps even a word about the purpose of the mail server and the number of users you have. That allows others to see that their time is well-spent and indeed leads to a working mail server. Thanks for …

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Troubleshooting your mail server

General troubleshooting tips Run “postfix check” to make Postfix look for obvious configuration errors. If it returns no output then no problem was found. Read your /var/log/mail.log and look for warnings and errors. Postfix keeps unwanted emails in the queue Check that you do not keep soft_bounce enabled. If “postconf soft_bounce” shows “yes” then run …

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Filtering out viruses and malware

My usual rant: I consider virus scanners snake oil. If anyone wants to seriously infect a computer by sending an infected attachment then virus scanners won’t help you. They are based on patterns of known malware and (if you are lucky) a working heuristic algorithm trying to detect unusual behavior. It has been proven time and …

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Filtering out spam with rspamd

You have a perfectly working mail server by now. But before you go live let’s do something about the insane amount of spam. In previous editions of this guide I used and recommended SpamAssassin. However I have found a piece of software that is more versatile, scales better and is still easy to integrate: rspamd. rspamd has …

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DNS MX records

About MX entries So now you have your working mail server. But how do other mail servers get to know you? The answer lies in the most important service on the internet: DNS. Assume that a mail server somewhere on the other end of the internet wants to send an email to john@example.org. The server …

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Testing email delivery

So far you have spent considerable time with theory and configuration. Are you worried whether all you did actually leads to a working mail server? Before we do the final steps let’s take a break and verify that everything you did now works as expected. At this point the /var/vmail directory should be empty or maybe contain an …

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