Doesn't Work Anymore

Had this plugin for almost 2 years and in the past 3 months it started to play up majorly. It stopped sending out email notifications to subscribers when I publish a new post, or it only does it when it feels like it. When readers subscribe, it no longer sends them a confirmation email to activate so I have all these unconfirmed email addresses sitting there useless both on my end and theirs.
I even had my domain host alter things from their end to rectify the problem but nothing worked. Shopping for another service now and what a pain cos I gotta integrate all my existing subscribers over to the new one without inconveniencing them…or losing any. What a mess!