I use Agent as my E-mail/newsgroup reader, actually I've always used Agent starting with version .98 (so know of no other similar programs); at this time Agent 6 as it has SSL. While I prefer 1.93 it hasn't SSL and the latest update to Stunnel not only didn't work, neither will the older versions now.
Agent won't load HTML, allowing you to read your E-mail as text; most HTML E-mail have two "versions" the HTML followed by text, both saying the same thing. Agent will load your E-mail in your browser if you want, but I have rarely needed to.
I can tell if an attachment has been sent with the E-mail by it's flags (status), the first item listed before the lines the message has, subject, author, and date. If I don't know the sender I just delete it by right clicking on the line of E-mail info itself. Since I've already downloaded it, if I really wanted to I could go into my incoming directory and see what it is, but if an unknown sender I couldn't care.
Charter offers access to the newsgroups (UseNet) as part of it's service (no charge) which I use Agent for as well. I've begun to notice people referring to Google Groups as the newsgroups (not even close).
Headers, while not as informative as they used to be (senders IP address no longer listed) are fully listed and an option to view along with the message. None of the E-mail programs I've seen (cell phone and such) have more than a few lines and of no real value.
I see E-mail having bounced back and forth between Google servers much like ping-pong. Servers which btw use the 10.0.0.0 ip address block Https://tools.ietf.org/html/rfc1918, all internal to Google. I was kind of impressed, cost em nothing.
I'd post one of the headers here but it would have to be edited to senselessness as it shows the complete path the E-mail followed; being forwarded E-mail, just too much info.
The only down side of Agent I've ever encountered are the features and options one has to work with, which can be overwhelming at first, this includes the message filtering system.
Not being that bright, a filter can take me quite awhile to get it to do just what I want, whether it's to begin downloading a file showing up sight unseen, or deleting one. The last time was to keep the first .par file but delete any additional .par files (ones needed to repair) as the newsgroups are very reliable, yep it took awhile.
But don't forget web based E-mail is a threat as well.
Feel I need to add: I have nothing to do with Agent (Forte), just a user.