Validating mx record
If the connection fails, your mail server should then attempt to connect to the next server.
As an example, here are the associated MX records for the domain microsoft.MX preference = 10, mail exchanger = maila.MX preference = 10, mail exchanger = mailb.MX preference = 10, mail exchanger = mailc.In this example, all of Microsoft's mail servers are weighted equally (10), thus your mail server will make it's own determination which mail server it wants to connect to first.
Enabling deep check will slow down your script even more as it searches the given server for 3 additional types.
will also match international characters that exist in some domains.
Please be aware this will likely slow your script down.