Sets permitted methods of SASL authentication for SMTP clients. Supported methods are:
Sets the SMTP protocol extensions list
that is passed to the client in response to the
It makes sense to specify the extensions supported by the MTA to which the clients are proxied (if these 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 www.iana.org.