Sending Email from my application cause an exception

0
votes

I have an application that send email for my issues. I use SmtpClient class for this work. It works fine with one of my mail servers but recently I use an exchange server for sending mail. my SendEmail method throw an exception with this message:

550 Requested action not taken: mailbox unavailable / 5.7.1 Unable to relay

Is this problem from my application or is it for mail server configuration? What is the solution?

1
c#asp.netsmtpexchange-server
100% I send an email on server that this mail exists. – masoud ramezani

1 Answers

3
votes

Well SMTP error 550 is generically (based on a little searching) define as something like:

550 Requested actions not taken as the mail box is unavailable.

This is likely an error at the destination. Eg. a disk drive has filled up.

In your case:

550 Requested action not taken: mailbox unavailable / 5.7.1 Unable to relay

The suffix indicates:

  1. The email is not hosted on the SMTP server you're communicating with.
  2. That SMTP server is refusing to forward to the final destination (or another relay).

There are many possible reasons for #2 (eg. an ISP's SMTP server will only relay when sending from inside the ISP's network) but finding out which would need to get into specifics (and it could be a temporary situation like loss of connectivity). Best to talk to the administrator/support for that server.