We send out large quantities of email to our customers (work environment surveys). Sometimes our mailinglist for a client isn't quite up to date and we get bounce mails (address not found and such). However, since these all bounce back to the same address it's difficult to keep track on which bounce belongs to which client. (The email subject is usually pretty generic, like "Welcome to the work environment survey")

This is why I would like to insert a identifier in the subject line of the email. So the subject would be "Welcome to the work environment survey (1234)" where 1234 is a number identifying the client/survey. We already rank pretty high because of the way our mailer handles sending the mails. Usually we contact the clients it-dept to get them to whitelist us in their firewall/spamfilter. Would this increase our spamscore in spamfilters?