Almost all mail providers offer some sort of mail collection feature via POP3 which can be used as an alternative to mail forwarding. The disadvantage is that y

Almost all mail providers offer some sort of mail collection feature via POP3 which can be used as an alternative to mail forwarding. The disadvantage is that you'll have some time delay (depending on how often your provider allows you to fetch mail). The advantage is that you aren't relying on any feature of the old mail provider. As long as it still provides POP3 you're all good - and I find it unlikely that yahoo will disable POP3. (not saying this to justify Yahoo's rogue move here, but to give advice to people who have this problem)