What is meant by "prefix" here in this context? what is the synonym?

Question

oPrefix the subject of each message to let the recipient know if an action is required.

Answer 1

Prefix=add a prefix to (ie. RE: or FWD:)

Synonym=prescript

Answer 2

In this case, I assume "prefix" means to add or attach something to the beginning of the subject. This is not the most common usage of the term, but it is still fully acceptable; "prefix" is defined as "a word, number, or letter placed before another," or "to add something at the beginning as a prefix or introduction."

Possible synonyms: add, attach, affix, adhere

So in context, this probably suggests using an action-oriented word at the very start of the subject line.

Answer 3

Attach to the beginning of the message. A synonym might be:

affix, tack on, append, or even connect