CC and BCC not delivery Email

Thanks, Old Toad, let's say I boot into Safe Mode, test it and it works, then reboot normally and it still doesn't? Or if it doesn't work in Safe Mode? The issue is certainly with Mac Mail, is there a reset option for Mac Mail to set it back to default?

I am still testing this iMac, the customer believed it is something I had done that has caused the issue, lol. until I said try it on the old Mac where we transferred the data from using Time Machine. It did it there also.

However, today I receive an email where I was CC from the client, almost 48 hours later, it is the only one thus far. This is only doing this in Mac Mail, not anything else. Very strange, but I had issues with the autocomplete, that not all entries came across, Apple said they should have, but they didn't even when I manually do them they still all didn't copy across. Mystery??

Personal Domain email. The server side has been checked and the emails have been tested thoroughly without error. It is only on the old iMac and the new iMac this problem occurs, I am guessing this issue just came across from the old machine when the data was transferred.

Just wanted to give an update on this issue, as I was constantly having a printer issue as well as the CC and BCC email issue. However, I had a light bulb moment and thought about the differences between the old and new iMac. The difference being that the customer wanted to change her Apple ID as she was sharing her husbands one. So after the transfer of data was done, a new iCloud account was created for the new iMac, however, the old Apple ID was controlling the updates etc. As I was also having an issue with a printer I decided to check the Apple ID, which was the old one. So log in as old Apple ID, so I could sign out of it. Then added the new account and wham bam thank you, mam - is appears to have solved the issues, not only with the printer but also with the email. The printer issue as not printing certain PDF's and Brother Printers was unable to help and just said it was a MAC issue which brought me to my light bulb moment. Your thoughts on this, please.