How to mask a link in an email?

Question

Email Marketing

The task is the following..
We have already sent a letter out of bounds (esp) to smtp for further sending to the world.
The letter contains a link aaaaa.ru the task is to mask the link to bbbbb.ru before it is received by the final recipient.
This, of course, is done by (esp) - but the letter is already outside the system.
We can use any server relay pads with trackers, for example.
Advise any simple solution for tests, without writing a program.
Maybe a ready-made system, a script for mta. We can use only our own implementations, not other people's mailing systems

Answer 1

Will the option "disguise as a word" suit? "a href="link"" word "/a"
(" " replace with < >)