Voor verzending van E-mail staan onze mailservers poort 587 toe.
Dus poort 25 is niet meer toegestaan.
Wijzig dit desnoods in uw mailprogramma of app.
Als dat niet kan, dan kunt u niet met onze mailservers verzenden.
Ports 465 and 587 are intended for E-mail client to email server communication sending E-mail.
Port 465 is for smtps
SSL encryption is started automatically before any SMTP level communication.
Port 587 is for msa
It is almost like standard SMTP port. MSA should accept email after authentication (e.g. after SMTP AUTH). It helps to stop outgoing spam when netmasters of DUL ranges can block outgoingconnections to SMTP port (port 25).
SSL encryption may be started by STARTTLS command at SMTP level if server supports it and your ISP does not filter server’s EHLO reply (reported 2014).
Port 25 is used by MTA to MTA communication (mail server to mail server). It may be used for client to server communication but it is not currently the most recommended. Standard SMTP port accepts email from other mail servers to its “internal” mailboxes without authentication.