In my line of work, I frequently send out emails with subject lines that include customer names followed by internal help desk reference numbers.
A fictitious example might be:
“Citibank 100 Main St New York, NY Video System Q# 1350400”
What are the odds that some of my customers might be filtering these emails due to their resembling or fitting patterns for spam?
Having my reference number in the subject line is handy, but I could start putting it in the message text if I have to.