Smtp email error: bad sequence of commands. The server response was: 5.5.0 recipient already specified

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I am using the

SmtpClient

to send automated emails in my application.

When I specify the "To Address" and a "CC Address" that are the same, the SMTP Client class throws the following exception:

Bad sequence of commands. The server response was: 5.5.0 Recipient already specified

I do not understand this error. I can manually write an email where the "To" and "CC" are the same.

What I have tried:

I have searched for this error on the web and cannot find anything.

Posted 8-May-24 6:13am

Kevin Brady

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Andre Oosthuizen 8-May-24 12:40pm

Please show us your code you are using to understand where your code errors. As it stands now it is a question in the dark.

Kevin Brady 8-May-24 12:54pm

It is too long to post here.

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Dave Kreskowiak · Accepted Answer · 2024-05-08T06:44:00

Solution 1

Seriously? It's telling you is that you have duplicate recipients. Just remove the duplicated recipients and the error goes away.

It is absolutely useless to send an email to the same user using both the TO field and the CC field, so just don't put the user emails in both fields.

You can do it in your email client because the client is filtering out the duplicated addresses when it posts the message to the server.

Posted 8-May-24 6:44am

Dave Kreskowiak

Comments

Kevin Brady 8-May-24 12:57pm

I disagree that it is "absolutely useless". And I don't understand why the smtp client should even care.

This is being implemented programmatically. Now I have to insert a check for it for duplicates.

Dave Kreskowiak 8-May-24 12:58pm

Why on earth would you specify the same email address twice in two different fields? I just don't see the reason for it.

You're not disagreeing with me. You're disagreeing with the server. You have to follow its rules, not mine.

Kevin Brady 8-May-24 13:04pm

Dave, Thanks for your help on this topic. I agree, I am not disagreeing with you.
One possible reason is that some email users filter their inbox based on whether they are "To" recipients or "cc" recipients.