Multiple emails sent when same email address is used in To, CC, and BCC fields

[ihimv]

If the same email list is passed in to, cc and bcc parameters, all the recipients get the same email 3 times.

The expected behavior is that even though the email addresses are repeated in the to, cc and bcc parameters, they must get the email only once.

This issue was found on Mailjet.Client, Version=1.2.2.0 running on .NET Core 3.1.

[sdiakovskyi-gd]

Hi @ihimv, Thanks for the ticket!

This behavior is not specific to dotnet library, but rather an implementation-specific detail of Mailjet servers. SMTP RFC does not specify deduplication mechanics, so some servers and clients try to duplicate, and some don't.

I'd suggest implementing the logic of deduplication in the client code (basically, don't add an address to CC if it's present in TO filed, and the same with BCC) Also, using deduplicate campaign field might help: Note: If you are using Mailjet as an SMTP relay, you can avoid sending duplicates emails to the same recipient with our custom email headers. Any duplicates will be automatically blocked by Mailjet.

If that's not the case, please, open a support ticket to direct an issue to the API team.