Unable to log into email account: Multiple password values not supported

Symptoms

Attempting to log into an email account results in the following error being written to /var/log/maillog:

Apr 9 14:32:42 server dovecot: auth-worker(123456): Error: conn unix:auth-worker (pid=123456,uid=97): auth-worker<12>: pam(user@domain.tld,203.0.113.1,<dYh3cS/b+revF/K>): Multiple password values not supported

Description 

If the server is running Imunify360, its Exim and Dovecot bruteforce protection feature can cause the "Multiple password values not supported" error when logging into email accounts.

Workaround

If you believe that blocked attempts to log into affected email accounts are legitimate, whitelisting the user's IP address may prevent the issue. This can be done in the WHM -> Imunify360 plugin interface:

WHM -> Imunify360 -> Firewall -> Whitelist

The Imunify360 team has indicated that disabling PAM protection for Dovecot may also help:

imunify360-pam disable-dovecot  

imunify360-agent config update '{"PAM": {"exim_dovecot_protection": false}}'

Disabling Imunify360s Dovecot bruteforce protection, at least temporarily, can help determine if this feature is the cause of the issue:

WHM -> Imunify360 -> Settings (the gear icon in the upper left of the interface) -> Uncheck "Exim+Dovecot brute-force attack protection" -> Save Changes