As usual Carol's on the ball.
I've run my own domain for about 15 years, sometimes hosting and sometimes forwarding to an ISP account. Over time spammers forced the creation of several free accounts to sign up for stuff. This was a popular notion in those days.
The problem with that is I need to know which email address relates to which newsletter or software purchase, sometimes years later. I used to keep a copy of the registration confirmations in sub-folders of a folder called "Registrations" which was automatically backed up in several places. It worked well but I got lazy and just saved the downloaded emails in my email software. (Usually Thunderbird or variations.) This worked fine and was always backed up but I'm a backup fanatic and try out pretty much anything I find. Sometimes I sync instead of backing up which tends to lose all my email, carefully saved for maybe a year or two.
Now I use Gmail, because I can't stuff it up. It also handles spam almost perfectly. In theory I'll never lose my Registration info again!
For the last year or so I've used a free address provided by Fanmail for all sign ups, using my own domain address for people I know. There has been no noticeable spam to the Fanmail address. In fact, over many years I've rarely, if ever, been spammed as a result of signing up for something (and I've signed up for a lot).
There used to be a bit of spam due to putting a business web address in the phone book but mostly it's ISP related. The bigger the ISP I use the greater the volume of spam, and I never use or give out an ISP provided address.
For me Gmail has been a godsend. (Yahoo was far less effective.)
For anyone wondering why I now use a big ISP, no-one else can give me Wireless Broadband. Satellite is unreliable and slow and dialup is just slow. The trade off is living in a beautiful and remote wilderness.