Don't understand what you mean errors in the database? Can you see that the email addresses are malformed?
If it's worked for 15 years (which as I said I'm amazed) and nothing has changed then I don't think the problem you are having now is with your data. I would guess you've pissed off your...
To be honest I'm quite surprised these messages have ever worked to be honest.
If I'm reading this correctly you are sending an email with an attachment to 250 BCC'd 7 times?
My guess is your service provider on your side has restricted you sending due to the suspicious activity.
Who is your...