I am currently having serious issues purchase order emails that the supplier says they have not received, yet we also copy the same PO at the same time to ourselves (and we receive it).
We send this supplier many Po's per day and it is only one or two (per month) that they say they do not receive (despite us receiving our copy).
It happens with PO's that involve the same drop ship customer (we tested today and they did not receive it three times yet we did).
We can forward the email PO from our account to them and they receive it fine.
We know QB's is sending it out (as we receive it)

We know that the supplier receives all other email PO's

The supplier is blaming QB's and says its not on their email server , its not in any junk or spam folder.
It causes us major issues as we assume it has been received and sent out and only when our customer calls to say they haven't received the good s do we determine that the supplier hasn't received it?
Any suggestions as to the cause?
Thanks