[j_maffe]

Not sure what you mean by blackmailing but it can't be the right word here.

[3form]

Feature A exists for years. New feature B enters. If you want to opt out of feature B, you now need to opt out of feature A as well, which you probably liked much more.

I don't know a better term than blackmail to describe this. Thesaurus seems to imply blackmail is for money, but so is extortion, and it doesn't give me good suggestions.

EDIT: Coercion is more correct, but it's way too mild in my perception.

[baggy_trough]

That sounds extremely dramatic when what we're talking about is features in a mail program.

[Zambyte]

A little malware is still malware.

[baggy_trough]

It is not malware at all.