I can see it from both sides. My gmail accounts (regular and throwaway) were roughly my fourth generation email addresses. I got my first email address in 1990. It was tied directly to an educational institution. When I switched institutions, I switched email addresses, and around that time got an ISP email address as well. Non-educational emails went to my ISP address and anything educational related went to my new edu address; everyone in edu circles knew to switch addresses because my .plan file associated with my old account advised them it was closed and what my new one was.

Eventually, I realized that neither my ISP nor edu institution would be with me forever, so I switched everything over to an email redirect service with Yahoo and Hotmail throwaway addresses for stuff that needed an account that was neither professional nor personal.

Then along came Google, Yahoo imploded, Hotmail got bought by Microsoft, and my email redirect service went out of business as the dot com bubble burst.

Oh, and I changed jobs which required moving which meant switching ISPs.

So GMail was a lifeline because I set all my other accounts to both forward to gmail AND set autoresponders informing the sender of my new address.

Of course, that happened 19 years ago. Back then, there were no SMS authentications, no real life accounts tied irrevocably to an email address. My eBay and PayPal accounts just needed an address update, and pretty much everyone else hadn’t got to the point where email address was even an option on a registration form.

That said, I recently did some email address shuffling, and all the accounts that really matter got switched relatively painlessly; I have a password manager, and part of changing addresses involves going through every entry in my password manager (which is already helpfully divided into personal, professional and throwaway) to update addresses as appropriate.

Everyone else gets the same autorespond and redirect treatment for a year. After that, anyone I’ve missed will have to locate me via someone else.

Of course, I’ve also maintained a PGP key since 1993 that has my chain of email addresses associated with it, so anyone who knows my key can just look up my current email address. It’s really the only thing I use that key for anymore. But there’s a very limited set of people that would even think to look me up by PGP, or even save a copy of my public key and remember the key exchange I use.

I had a similar history but I went through the process anyway. Got my own domain and used Fastmail for hosting. I like their masked email address feature. It’s taken months but I went through one by one and changed all my important email addresses. There are a few that can’t be changed though, and some services that I signed up with using my google account also can’t be changed. It was still worth it. Calendar isn’t a big deal to change either. I forwarded all my email to Fastmail and also subscribed to my google calendars to make the transition easier.