Sets permitted methods of SASL authentication for SMTP clients. Supported methods are:
Allows to specify the SMTP protocol extensions list
to be passed to the client in the response to the
It makes sense to specify extensions supported by MTA to which clients are proxied (if this extensions are related to commands used after the authentication, when nginx transparently proxies the client connection to the backend).
The current list of standardized extensions is published at the www.iana.org.