I have Eudora 7.1 for Windows. When I try to send a message I get a popup window that says, "Server SSL Certificate Rejected" and they says "The server's SSL certificate was rejected for the following reason: Unknown Error. Do you want to trust this certificate in future sessions?" Clicking Yes to this question accomplishes nothing.
There were a bunch of older postings about Eurdora about a year ago. There was some setting that had to be changed in one of the control files back then. Had to do with the advertisement of a security option which couldn't be used with the Veriozn Servers. The same problem may be back.
I downloaded Eudora 7.1 and I also get the same error message. I saw also on Qualcomm's website, link below, that they transitioned Eudora to Mozilla...makers of Thunderbird. I doubt this problem will be addressed by Verizon as Eudora has long been retired.
I did download the Thunderbird email program and that worked fine for me.
I had the same outgoing problem with Eudora 6.2.4 for Mac last week. Today (8/31/15) the problem got worse: I can't receive mail either. (About a year ago I fixed the SMTP authentication problem with a solution I found on the forums by clicking on <x-eudora-setting 12909=CRAM-MD5> in an email.) But I'm suspecting the current problem is an expired certificate, or two.
I had used Eudora for so many year, and within the last year, the program just got too wonky for me. Between issues of sending and receiving, the certificates, and then when I would start up the program, had to click check mail program twice for it to work. I switched to Thunderbird, and imported all my Eudora files, settings and mail. I am so glad that I did it. It took me a day to set it up just the way I want, and now, my mail issues are gone. Eudora was great when it was supported, but now, it is just way to much of a mess to use.