I'm also a little surprised to hear of your site incompatibility troubles with Safari. I, like a few others who also left comments, have run into very few problems in that regard. Safari works fine with my banks web site, as well as Chrysler Financial and some others you might expect to have problems with (but I don't). Regardless, I hope you find a more workable (and native) solution to your problems.
BTW, my wife has been using Thunderbird/Lightning for a good while now and it has worked well for her.
I still have my 2000. Don't use it much these days, but I still fire it up once in a great while and chuckle at the severely pixelated cheesecake shots of Brooke Burke I still have stored on it. Unfortunate noone could successfully realize the potential of this great device. A victim of being too far ahead of it's time.
"You were in second grade when the iMac G3s were around? Gawd, I feel old."
No kidding, same here. The first I ever personally owned (I had used my schools Apple IIc before that) was an SE/30 that we inherited in '89 after my mother-in-law, who had more money than sense, bought it and then decided her Olivetti typewriter was easier to use. Hours of fun with MacPaint. That was followed by a used IIcx with a funky monochrome portrait display that my wife used to write school papers. Good times, and a world of discovery watching as all this new tech unfolded.
Why I Wish I Could Use Safari (and Other Task-Focused Mac Apps)
April 4, 1990: Sculley Bets Big with the Newton
My Apple Switch Story