Well, with almost 30 email addresses in use on my iMac, I guess I count as a "power user" - I don't have all of them feeding to my phone, iPad or MBP, since some of them are strictly related to particular domains and mail received on them is usually to do with hosting or domain renewals, SSL certificates etc. (ie: work related) Why so many? Well...it has to do with getting deals for clients for web hosting (have to keep being a "new customer") as well as having to use domain-associated email addresses for things like SSL certificates etc. And email from contact forms on websites that I manage on a volunteer basis all has to be kept separate, and many of those organizations have Gmail accounts as well, which a number of us access. I wouldn't want to use a personal email addy for any of those situations. I have 4 tiers of my own email addys: personal (family/friends/clients), personal + license registration/some clients (that's a Gmail one), email addy used for signing up for mailing lists (Gmail again) and complete junk - a Yahoo address I rarely bother checking online and don't even have in Apple Mail. Oh and then there are two email addresses attached to my own personal domain (rarely used, though one is for the contact form on my site) and the iCloud one I never use either. And a spare Gmail account I used for another website hosting as a new user sign-up.
I use Apple Mail - it works just fine, in my experience. There are over 34,000 messages stored in my Inbox and my Sent folders - and that's not counting the older stuff that's in folders offline. Yeah...that's a lot of email.
I used to use Entourage, but switched about 10 years ago when it started to get corrupted rather too often.
And yeah, in case you're wondering, I'd be completely lost without 1Password. There are over 900 passwords in that.
