Posted inmta postfix smtp

Postfix smtp outgoing load balancing

I got good workaround for balancing smtp outgoing from postfix mailing list archives(not using expensive real load balancer). suppose we have 4 smtp servers for outgoing email, and we need to configure/load balance like this:

                                                         +------------+
                                                         |            |
                    +----------> smtp backend a -------->|            |
                    |                                    |            |
clients --------> smtp lb -----> smtp backend b -------->|  Intenet   |
                    |                                    |            |
                    +----------> smtp backend c -------->|            |
                                                         |            |
                                                         +------------+

Here’s the configuration :

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Posted inesmtp smtp

Extended SMTP

Extended SMTP

Extended SMTP (ESMTP), sometimes referred to as Enhanced SMTP,is a definition of protocol extensions to the Simple Mail Transfer Protocol standard.
The extension format was defined in IETF publication RFC 1869 (1995) which established a general structure for all existing and future extensions.
ESMTP defines consistent and manageable means by which ESMTP clients and servers can be identified and servers can indicate supported extensions.

Extensions

The main identification feature is for ESMTP clients to open a transmission with the command EHLO (Extended HELLO), rather than HELO.

Some relatively common keywords (not all of them corresponding to commands) used today are:

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Posted insmtp

The Difference Between HELO and EHLO

EHLO indicates that the client supports at least one of several possible extensions that are not part of the basic SMTP specification. HELO indicates that it does not, and that only the minimum SMTP set will be used when talking to this server. Many of these extensions are common and…
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