SMTP (Simple Mail Transport Protocol)
SMTP is a server-first protocol, with one additional capability. For improved security, an SSL client can request that an SMTP connection is encrypted using SSL (also known as TLS).
If you configure a virtual server to use the SMTP protocol, it behaves like a regular Generic Server First protocol (for further information, see Server-First Protocols). Ivanti recommends you configure your virtual server with a server first banner. For further information, see Server-First with "Server Banner").
Note that if you enable SSL for an SMTP virtual server, the Virtual Traffic Manager provides an additional setting named smtp!expect_starttls on the Virtual Server > Edit > SSL page. Configure this setting as follows:
- No: The virtual server decrypts SSL traffic in the normal way. In other words, expect traffic to be SSL-encrypted at the very beginning of the connections.
- Yes: The Virtual Traffic Manager processes traffic in plain text, as if it were unencrypted. The Virtual Traffic Manager watches for a “STARTTLS” SMTP command from the client and then initiates an SSL handshake to upgrade the client’s connection to SSL.
The Virtual Traffic Manager forwards all traffic to the back-end SMTP servers unencrypted (in plaintext) unless you enable SSL encryption in the pool configuration. If you enable SSL encryption, the Virtual Traffic Manager encrypts the connection from the outset, rather than using the STARTTLS SMTP command.