The Dovecot pop3 mail server throws an error when I executed the openssl s_client command to verify the server settings. This error only is produced when I use the pop3 protocol, not when I’m using IMAP.
My server is configured to use virtual mail users for mail delivery. E-mail is stored encrypted server side using the mailcrypt plugin (https://wiki2.dovecot.org/Plugins/MailCrypt). The server is using valid SSL certificates to encrypt the connection. I have played around with the disable_plain_text_login setting, this did not have effect on the behavior.
When I execute “openssl s_client -connect mail.server.com:995” it connects fine. Providing the username works, when I send the pass command the following entry is shown in my log:
Nov 10 16:29:02 vmi1040354 dovecot[26845]: **pop3(USER_NAME): Error: Couldn't load required plugin /usr/lib64/dovecot/modules/lib30_imap_zlib_plugin.so: dlopen() failed: /usr/lib64/dovecot/modules/lib30_imap_zlib_plugin.so: undefined symbol: imap_module_register**
The referenced module is available and both 20-imap.conf and 20-pop3.conf point to this zlib plugin, yet only pop3 throws this error.
What can I try to fix the issue and get pop3 to work?