Can I make for better delivery of letters?
To data for User-Agent and X-Mailer were taken from a text file .
For example in 1000 a mailing list User-Agent or X-Mailer = 100 - they are taken from the file and rotated or randomly.
Yes but your list contains mostly web browser agents... :-/ for email the list is quite limited and in most cases either you use the one of a known application or none at all...