One thing I soon learned was that the legit things that you sign up for are not the problem, it is the ordinary people who you email who don't protect their PCs.

When running a mailing list I shifted it to a new address on buying a domain. After the first mail out from the new address I was getting spam to the new mailbox.

When I was involved as webmaster for an organisation I used a two step system to keep spam out. 1/ Use a spam filter on the domain. 2/ forward to a webmail account with its own strong filters such as Hotmail.

To protect mailing list recipients I used a totally different email client to run the mailing list.

Once every few months I would switch the filters off for a week and plough through the spam to check for false positives.