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421 SMTP service not available

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3 replies

by edmond_sng

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Lately, we have been experiencing some problems with sending mail to one particular address. We tried to telnet from our SMTP server and comes back with a
421 SMTP service not available, closing transmission channel
Connection to host lost.However we could telnet from other mail server at different network. Please advice. Thanks !

3 replies

by chucksa

Simple Mail Transfer Protocol (SMTP) is a TCP/IP service run at the application layer. This service may not be enabled on the server you are trying to access.

Telnet is a separate protocol of TCP/IP and is used to connect to a remote computer and run programs or view files.

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