Typical choices
IMAP usually uses port 993 with SSL/TLS, POP3 uses 995 with SSL/TLS, and SMTP submission uses 465 or 587 depending on client configuration.
Avoid unencrypted login and old settings left after migration.
Domain security
Mail ports are only part of the setup. SPF, DKIM, DMARC, anti-spam and spoofing protection are also important for domain reputation.
Hostilla.pl combines e-mail configuration with anti-spam, antivirus filtering and user reports.