Which SMTP Port to Use?
For email services there are many different SMTP ports to use for sending emails, below are the most recent ports and reasons for use.
This port continues to be used primarily for SMTP relaying. SMTP relaying is the transmittal of email from email server to email server.
In most cases, modern SMTP clients (Outlook, Mail, Thunderbird, etc) shouldn’t use this port. It is traditionally blocked, by residential ISPs and Cloud Hosting Providers, to curb the amount of spam that is relayed from compromised computers or servers. Unless you’re specifically managing a mail server, you should have no traffic traversing this port on your computer or server.
IANA has reassigned a new service to this port, and it should no longer be used for SMTP communications.
This is the default mail submission port. When a mail client or server is submitting an email to be routed by a proper mail server, it should always use this port.