The Yahoo spam hit is because all their, Yahoo’s, account details for every user were stolen (all 3 billion).
The easiest answer is to just send them to junk and even the move to gmail will not absolutely rid them, @Wend, of spam. Addresses get stolen all the time and eventually their gmail address will be added to spammers lists. They may enjoy a honeymoon period as they start to use the new account but it may be very short.
Sending junk mail to spam folders actually has a use, it allows the mail provider to adjust their filters. If using Outlook (Office program not the live mail) it allows them to update the filters they send out as updates to the program. The period for action to happen however can be lengthy.
Also Yahoo is no longer it’s own company, it is now owned by Verizon and I would hope they are more proactive about security and spam than Yahoo seemed to have been.
