I got the following error after sending out an email to one account:
554 error [numbers .mxlogic.net] (Mode: normal)
Has anyone had the same issues and know what the cause is?
MXLogic is an anti-spam service that has ceased operation. It's quite possible someone forgot to change the MX records for a little-used domain that still points to MXLogic. Impossible to know if you don't provide the real address.