I've sent an important email that the recipient claims it wasn't received by them.
They say that they asked their IT team to see if the email was received in their server. According to them the email never reached their server. Also they don't accept the chance that the email was received and marked as SPAM.
Shouldn't I receive an error message in the case the email wasn't delivered?
Is their any way for me to check if they are telling the truth (it sounds very fishy to me).