Smart host

As an SMTP relay server, mail relay server or smart host is a mail server called (B ), which takes from a transmitter ( A) e-mail and to any third party (C ) forwards.

A correctly configured SMTP relay server ( smart host ) manages emails continue only if he

• Is responsible for either mails from A

• And / or is responsible for mails to C

An uncertain configured SMTP Relay Server is a so-called Open mail relay and forwards e-mails continue, where he is still responsible for neither C for A. Such mail servers are abused by spammers to mass spam mailings and are then often placed on blacklists as DNSBLs. Not only actual mail server, but also members of botnets can represent open relays.

Use

Relay server for e -mail programs

SMTP relay servers are used primarily by e -mail programs to send emails. In certain cases, this requires registration, see SMTP Auth and SMTP - after- POP.

Relay server for mail server with a dynamic IP

Mail server with a dynamic IP address must not consign for many recipients who sent e -mails run the risk of being filtered out by spam filters. To circumvent these problems, the sender can use a relay server with which the recipient is considered to be trustworthy. In general, the transmitter before using the relay server cf. SMTP - Auth and SMTP - after- POP must be authenticated at this.

Relay server for specific purposes

Offers for online spam filters and online virus filters are usually implemented with relay servers. Before the e-mail is delivered to the mail server of the receiver itself, it passes through the relay server, and is there filtered.