Port 25

Q: What is port 25?

Email transmission between mail servers SMTP on port 25 is the foundation of email on the internet. It is used exclusively for server-to-server communication (MTA to MTA). ISPs almost always block outbound port 25 from residential connections to prevent spam. For sending email from an application or client, use port 587 (SMTP Submission) or 465 (SMTPS). Checking whether a mail server has port 25 open is commonly done when debugging DNS MX records.

SMTP

Email transmission between mail servers

Port

Protocol

TCP

Service

SMTP

Security

Restricted

Full name: Simple Mail Transfer Protocol

What is port 25?

SMTP on port 25 is the foundation of email on the internet. It is used exclusively for server-to-server communication (MTA to MTA). ISPs almost always block outbound port 25 from residential connections to prevent spam. For sending email from an application or client, use port 587 (SMTP Submission) or 465 (SMTPS). Checking whether a mail server has port 25 open is commonly done when debugging DNS MX records.

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