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...