Module ngx_mail_pop3_module

Directives
     pop3_auth
     pop3_capabilities

Directives

Syntax: pop3_auth method ...;
Default:
pop3_auth plain;
Context: mail, server

Sets permitted methods of authentication for POP3 clients. Supported methods are:

plain
USER/PASS, AUTH PLAIN, AUTH LOGIN. It is not possible to disable these methods.
apop
APOP. In order for this method to work, the password must be stored unencrypted.
cram-md5
AUTH CRAM-MD5. In order for this method to work, the password must be stored unencrypted.

Syntax: pop3_capabilities extension ...;
Default:
pop3_capabilities TOP USER UIDL;
Context: mail, server

Sets the POP3 protocol extensions list that is passed to the client in response to the CAPA command. The authentication methods specified in the pop3_auth and (SASL extension) and STLS directives, are automatically added to this list if the starttls directive is enabled.

It makes sense to specify the extensions supported by the POP3 backends 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.