I have an issue regarding email fails which is it seems certain addresses cause my system to come back with errors which usually trips the defer rate error (note that these are valid email addresses).
I was wondering if there was any reason for this; the email extensions that usually come back with errors are AOL and Tesco which causes the system to shut down for an hour. This, as you'd expect, causes issues for us as we can't send any emails out for the next hour.
Is there any reason this is happening? Is there a problem with the route or the settings on their account or are these hosts just too strict with their filters?
Also, with the defer rate, when it says something like 5/5(20%) is the '5/5' bit regarding 5 out of 5 errors reached? Does the percentage refer to how many emails sent out in the past hour had errors?