Maximum number of connections from user+IP exceeded ???
I'm using a VPN on my computer and phone and when I try to connect to the mail server, Thunderbird gives me an error saying that the mail server has disconnected. But when I disconnect from the VPN, everything works. This happens only with one mail server, on the others everything works OK even via VPN.
However, the the mail from this server is coming to my phone (where I use K-9 Mail).
I also tried to connect to the mail server via openssl, with the command "openssl s_client -connect mail.server.net:993 -crlf"
The connection is successful (when I'm on the VPN), but when I enter the command "a LOGIN my.username MYPASSWORD", it gives an error:
a NO [UNAVAILABLE] Maximum number of connections from user+IP exceeded (mail_max_userip_connections=20)
I have set the "Maximum Number of server connections to cache" to 1 in Thunderbird, I have set to check for mail every 12 minutes (it already was 15 minutes on the phone before), and it is still the same.
Any idea how to solve the issue? I am connecting to this server with the same username and from the same (VPN) IP only from my phone and my computer, so I find it really strange that there are more than 20 simultaneous connections...
Chosen solution
OK, found the problem!
My mail provider spotted a log entry saying "Multiple password values not supported".
Then things became clear. The problem was caused by Imunify360. So provider whitelisted my IP and suddenly everything started to work. :)
Anyway, it is still mystery to me why there were more than 20 IP+user connections... maybe a bug in Thunderbird?
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If there is no error when not using the VPN, my guess would be the VPN has the limit to connections
No, I have my own VPN - I tried Wireguard and OpenVPN, but on the same server, so I guess it is IP related, and it is caused by the mail server (that is not my own).
And besides, how could VPN be limiting connections, if I establish a TLS session (with openssl)? Connection is established, just at the authentication phase then fail. Again, authentication to mail server - encrypted connection - so VPN can not see the traffic.
I also checked how many TCP sessions are open from my VPN server to the mail server (with tcpdump) - and basically, it is just one from my computer.
Chosen Solution
OK, found the problem!
My mail provider spotted a log entry saying "Multiple password values not supported".
Then things became clear. The problem was caused by Imunify360. So provider whitelisted my IP and suddenly everything started to work. :)
Anyway, it is still mystery to me why there were more than 20 IP+user connections... maybe a bug in Thunderbird?
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