~ email guide

SMTP Ports 25, 465, And 587

SMTP uses different ports for different jobs. Knowing which port is expected helps separate mail submission, server-to-server relay, and TLS policy issues.

Port 25

Port 25 is commonly used for server-to-server mail transfer. Many residential and cloud networks restrict outbound port 25 to reduce abuse.

Port 587

Port 587 is the standard message submission port for authenticated clients. It usually starts plain and upgrades with STARTTLS when configured.

Port 465

Port 465 is commonly used for implicit TLS SMTP submission. The TLS session starts immediately when the connection opens.