Hi @Sherazad Ahmed ,
The message you received, “No match in user info list. Input : <customer email>”, is a system-generated error message that indicates that the email address you entered is not recognized by the system.
The second message, “Beginning attempt 1 to send mail to recipients”, is a notification message that indicates that the system is attempting to send an email to the specified recipient(s) .
I wasn't able to reproduce your situation, I checked internal and external sources and couldn't find a reason for only one failure. And as per your description it seems that All the emails go out successfully, I guess the one that failed could be due to poor network or something else.
This may be an occasional incident, don't worry. Feel free to let us know next time this happens again.
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