my mailcow works behind a static IP (IPV4).
I’ve openend the typical ports in the firewall, i’ve made the DNS configuration and server records.
The cow works perfect from the most Networks (Private ISP, Home DSL, Smartphones and so on).
It works with Outlook, Thunderbird and other Mailclients.
But i have the effect, that from some Networks the mailcow isn’t available.
All trys to connect with Imap, Smtp, Web-Config over Port 443 aren’t working.
I get a timout.
For example i’ve set up an email-account on my notebook.
It’s working from everywhere fine, but from some normal ISPs or Networks i don’t get a connection.
A ping to the mailcow works ALWAYS from every network with the DNS-Names and with the static IP.
A traceroute also responds, and i can do a telnet to port 25…telnet ALWAYS answers correct with
“220 mail.xxxxxx.de ESMTP Postcow”.
In the mailcow postfix-Log always see "CONNECT from [“external IP-address”]:63541 to [172.22.1.253]:25″.
But when i try to connect FROM THE SAME network with my mail-software (for example Thunderbird), that works fine from other ISPs and Networks, i get a timeout.
Is it possible that i get this effect because i don’t have the the RDNS / PTR-Entry in my DNS?