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I have a vServer from Server4You and installed a mailserver with postfix, dovecot and slapd for authentification, my problem is: All the emails send from the server to outlook or gmail land in the spam folder, I did set a MX Record for mail.domain.tld an A record for my ip pointing to domain.tld, a second A record pointing from ip to mail.domain.tld and a TXT Record for SPF.

 v=spf1 a mx ptr a:mail.domain.tld mx:mail.domain.tld

Postfix is configured as smtp server for mail.domain.tld and emails will be send from e.g. test@domain.tld

A reverse DNS on my IP shows domain.tld but a DNS on mail.domain.tld returns the same IP (since they are on the same machine)

My question: How can I send emails from this server without them being marked as spam? Do I have to change the hostname on the machine to mail.domain.tld and if yes will this server still be available at domain.tld(for the web applications)?

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One thing the receiving mail server (if it checks for SPF) will do, is to simply check the IP that is connecting against the SPF entry, if it even exists. So if john@example.com sends an E-Mail, it doesn't matter, that a server called mail.example.com is greeting the receiving mail server, as long as the SPF entry in example.com allows mail.example.com to send e-mails in his name.

But the SPF-check is not the only check the receiver does to check for spam. Another one is from Postfix itself, where it verifies that the EHLO hostname (the hostname the connecting server identifies itself with) is the same as the reverse DNS hostname from the IP connecting and also that this hostname points back to that IP.

So what you could do, is to make sure that the mail server has the proper hostname set (it usually uses this for EHLO, but you can specify another one in main.cf), which is the same like the rDNS of the IP it uses to connect to other mail servers and of course that this hostname points to the IP. This doesn't have to be example.com, but could also be mail.example.com as long as the SPF allows for that. But you need to put this SPF record in example.com, since this is the domain where john@example.com belongs to.

For the SPF entry, I would recommend you to use IP addresses instead, since every hostname it has to check, results in another DNS request which slows down your e-mail processing. Unless you change your IP addresses rather often, there is really no need to use hostnames.

Example: v=spf1 ip4:192.0.2.1 ip4:192.0.2.2 ip6:fe80:123::4

You can add a and mx after the IP address, but it doesn't really make a difference if it points to the same IP anyways. By the way: if you don't want mails that fail the SPF-check to be rejected (this is usually the default), you can add ~all (notice the tilde) at the end too. If you want it to be rejected all together put -all instead.

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Now for the last part of your question: Yes, you can set the hostname/rDNS to mail.example.com and still serve webrequest over example.com.


I hope this was helpful to you.

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