SMTP Relay - what is it and how it works?

Hello friends,

I use Windows Send Mail Server and it uses SMTP relays server as what my mail server says when it is unable to send or forward message to whomsoever it may have sent,When I check for more details it shows that SMTP relay issues.

When we send Mail through user@gmail.com ID it does not give any issues and works fine. But when we send any e-mail msg from user1@rocketmail.com to user2@hotmail.com the mails goes to the drop mail folder of the SMTP relay server...

What could be the problem.....

SMTP Relay allows to send email messages through email account using existing email service.

For example, If we are using Microsoft Outlook to compose, receive, and send email messages, but actually email messages are processed through SMTP relaying services of whose services you are using. This allows to bypass ISP restrictions on the outbound email messages and allows user to use your professional looking "pracitse@example1.com" email address rather than a general “process@isp_name” address.

SMTP servers act as local post offices while transferring messages from one end to another. When a user ready and attached e-mail messages to send via email, he or she sends it to the SMTP server, which then forwards it to the appropriate recipient which is also a SMTP server. It may includes street address and apartment numbers, electronic mail recipients which may be identified as unique email address.
Most generally SMTP server is configured to handle one or more domain names. Analogous to snail mail, if both sender and recipient are in the same domain no other SMTP server gets involved.this is how the functioning of the overall SMTP relay.