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falcon7700
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Posts: 1
Joined: Tue Jun 15, 2021 7:49 pm

Mikrotik blocking 993

Tue Jun 15, 2021 8:14 pm

A strange problem has cropped up: After initially allowing port 993 outgoing traffic to my mail server, the Mikrotik starts blocking both 993 (imapSSL) and 465 (smtpSSL).
This is what a user sees using nmap when this is happening:
Nmap scan report for imap.th.net (52.15.184.56)
PORT STATE SERVICE
80/tcp open http
125/tcp open locus-map
443/tcp open https
465/tcp closed smtps
587/tcp open submission
993/tcp closed imaps
1022/tcp open exp2
8443/tcp open https-alt

To debug this problem, I cleared the config on this RB750G3 router, updated to the latest RouterOS, and used "webfig" to change only the internal IP address and DHCP ranges- leaving everything else default. So this should be as vanilla a configuration as possible.

Nmap scan report for imap.th.net (52.15.184.56)
Not shown: 992 filtered ports
PORT STATE SERVICE
80/tcp open http
125/tcp open locus-map
443/tcp open https
465/tcp closed smtps
587/tcp open submission
993/tcp open imaps
1022/tcp open exp2
8443/tcp open https-alt
I

If I reboot the router, both 993 and 465 show "open".
Another nmap run after reboot:
Nmap scan report for imap.th.net (52.15.184.56)
Not shown: 992 filtered ports
PORT STATE SERVICE
80/tcp open http
125/tcp open locus-map
443/tcp open https
465/tcp closed smtps
587/tcp open submission
993/tcp open imaps
1022/tcp open exp2
8443/tcp open https-alt

Now 993 is open and my mail client is happy. Any idea what is going on here? Some kind of buffering or overflow problem?

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