Here is a feature request/UI improvement: In the most cases when a new server certificate is deployed, the change affects both SMTP and IMAP/POP servers. Since people check mail more often then send it, a user would first observe a new certificate dialog for the check mail action, which will update the certificate for IMAP/POP endpoint. Now when the send mail action takes places, basically the same dialog would be posted that requires the same user actions. Claws could first check, whether the IMAP/POP and SMTP hostnames are the same, and if either of them has got accepted a newer certificate with the same checksums, hint the user that it is safe to accept the cert without a tedious checksum verification or even accept it right away on user behalf (perhaps configurable option).
> (perhaps configurable option) See the Account preference, "Automatically accept valid SSL/TLS certificates"