SMTPSocket.SendMail retrying 1000 times?

Hello all. I have an old Xojo application that I am about to update to the latest release. While emailing to external email addresses initially worked, it has been failing silently for a while now. What is concerning is that the email server log is showing 1,000 retry attempts. These retry attempts is my main concern. This email functionality works perfectly when sending email internally but not externally. Is there anything within Xojo that sets what the retry attempts are? I can’t find anything. Here’s the boiled down code:

// send the email
DIM MailSocket AS NEW SMTPSocket
MailSocket.Address = ""
MailSocket.Port = 25
CATCH err As NilObjectException
  self.LogActivity( "SendMailTo1", "LastErrorCode: " + CSTR( MailSocket.LastErrorCode ) )
End Try

I’m about to convert this over to Office365 and using a SMTPSecureSocket, but my bosses are concerned that failures to send an email would result in 1,000 retry attempts. Is there anything inherent in Xojo that controls this functionality? or is this built within the mail server? Thanks ahead of time.