Port 25 1

[IPDetective]

I hope there is someone out there who can shed some light. I have heard about port25 and services that can bypass port25. I was wondering if anyone would mind explaining to me what this is and if you can bypass this port by yourself. Without signing up for a service.

 

[jrbarnett]

Port 25 is used for SMTP mail transfer, normally between companies and ISP's, sending emails around the internet, which are then picked up by clients connecting to a POP3 service (port 110) after the message reaches the destination mail server.

Many ISP's restrict the range of IP addresess that can connect to their SMTP servers to send emails to those issued to their clients, as a means of preventing systems using them for relaying spam. SMTP mail relays where there is no restriction are called open relays, and are often used by spammers to transmit their messages, and as such it is a good idea for those responsible for email administration to ensure that the servers they run are properly locked down.
In order to get around this, some viruses include their own SMTP mail engine, so the messages get sent directly from the PC rather than the one on the network they use. The success of this depends on how stronly the network administrator has locked down SMTP traffic.
The SMTP protocols are freely available for anybody who wanted to write their own email server, which would bypass the ISP/company servers, but its success in being used in a particular environment would depend on how the network has been configured.

John