Just to clarify, do you mean a MUA for IMAP4 or do you POP3?
There are a lot of very nice IMAP4 web based front ends (eg: roundcube, etc) to use if you like having all your email out on the internet all the time. Tons of email account providers will offer a handful of these for you to use to access the underlying email stored on their server(s).
If on the other hand you mean a POP3 client and use ms windows, I'd recommend "The Bat!" as it is a very feature rich MUA. I've been using this software since 2003 and it's invaluable for researching back into my almost 20 years of email, is encrypted and I sync it with any other PC I use via SpiderOak. It's old school I guess, but I don't like the idea of my email sitting on a server out in the world for very long unless it's on SpiderOak... and having it all locally stored is nice at times when the internet isn't 24/7.
Tutanota is pretty slick but it's limited to web access only which I limit to trivial emails since I prefer the POP3 approach and personally securing my email.
If you have concerns for security and/or privacy and prefer to use IMAP4 access there are email account providers that can provide encryption at rest for your email store for some additional security if leaving email out in the wild.
If privacy and security are important you might want to look at Posteo or Mailbox.org for mail with POP3, IMAP, SMTP, more options -- otherwise Tutanota is a great web only email provider. There are lots of options and I'd suggest most all are well worth the time in breaking away from a huge ecosystems like google, microsoft, etc.
@SoCalGardener wrote:.
Ha ha ha!! I know *I* felt so clever and unique when I dreamed this method up in the early '90s. I'll bet each and every one of us who uses a similar method felt that way! But, yeah, elite is good.
Huh. I guess I'm elite, too. I use the method but also use random strings for the name before the @.
@Have1 wrote:
@SoCalGardener wrote:.
Ha ha ha!! I know *I* felt so clever and unique when I dreamed this method up in the early '90s. I'll bet each and every one of us who uses a similar method felt that way! But, yeah, elite is good.
Huh. I guess I'm elite, too. I use the method but also use random strings for the name before the @.
Yay! You're elite, too! 
The reason I don't use random strings is because I would never remember them on a per-site basis. In other words, when I log in on sites that use your e-mail address as your username, there's no way I could remember 5,000 different, random addresses. 
My method has worked great because if I go to ThisSiteIsCool.com, I know right away that the e-mail address I used is thissiteiscool[whatever]@mydomain.com (the [whatever] meaning whatever method I'm using then--I've used various things over time, like 'trap' or 'account' or whatever). Easy on the old gray cells, you know?! 
@SoCalGardener wrote:
@Have1 wrote:
@SoCalGardener wrote:.
Ha ha ha!! I know *I* felt so clever and unique when I dreamed this method up in the early '90s. I'll bet each and every one of us who uses a similar method felt that way! But, yeah, elite is good.
Huh. I guess I'm elite, too. I use the method but also use random strings for the name before the @.
Yay! You're elite, too!
The reason I don't use random strings is because I would never remember them on a per-site basis. In other words, when I log in on sites that use your e-mail address as your username, there's no way I could remember 5,000 different, random addresses.
I use a password manager for user names and password organization. I know some of my usernames and almost none of my passwords. I figure if you can remember a password it is, by definition, a bad (subject to dictionary attack) password. In any case, you don't have to be the fastest runner to get away from the bear, just faster than those with you when the bear shows up.
@Have1 wrote:
@SoCalGardener wrote:
@Have1 wrote:
@SoCalGardener wrote:.
Ha ha ha!! I know *I* felt so clever and unique when I dreamed this method up in the early '90s. I'll bet each and every one of us who uses a similar method felt that way! But, yeah, elite is good.
Huh. I guess I'm elite, too. I use the method but also use random strings for the name before the @.
Yay! You're elite, too!
The reason I don't use random strings is because I would never remember them on a per-site basis. In other words, when I log in on sites that use your e-mail address as your username, there's no way I could remember 5,000 different, random addresses.
I use a password manager for user names and password organization. I know some of my usernames and almost none of my passwords. I figure if you can remember a password it is, by definition, a bad (subject to dictionary attack) password. In any case, you don't have to be the fastest runner to get away from the bear, just faster than those with you when the bear shows up.
I keep a database of all my accounts and their usernames, passwords, anything pertinent about them. I let my browser (or app, as the case may be) save each site's username/password whenever possible. I only know a handful of my actual passwords, since I almost never need to type them in.