For the last couple of months my Optus email account has been drowning in spam emails compare to my Gmail account to which I am receiving little or no spam - this only just seemed to have escalated in February this year and now it at a point where I am spending at least half hour a day reporting and blocking the spam but all to no avail as just receive as many again the next day - I would say around between 20 to 40 spam emails a day - how do I stop this please?
You don't need to cancel the Optus address. Just leave it doing nothing. You can set GMail to automatically import all past and future emails form the Optus address (and auto label them) so you don't miss anything. Turn off the import once you're happy you have updated all contacts and institutions.