You may need to say specifically which 'settings' you checked. Specifically those for the incoming IMAP or POP server - compared with and checked against your email provider's preferred settings. If you see any error message or symptom when downloading does not happen - describe that too, to help people detect what's going wrong.

Thank you AgnesRM for your response! As to the settings I checked. I followed the guidance provided in the online Mozilla Support page that pertain to my issue. https://support.mozilla.org/en-US/kb/cannot-send-messages#w_reset-smtp-password

All my POP/SMTP settings match. The password used to access my email account is valid. I also deleted and reentered these settings and also went to far as to download and setup a new TB Portable app on my PC and set it up with my account information all to no avail. Additionally I moved my app via SD Card to a different PC which again made no difference.

TB will show it's connected to my provider's (IONOS/1&1) server in the bottom tray sometimes freezing in the process but more often after an interval disconnects without downloading any new mail.

I'm also very confident this is a TB issue in that I continue to receive and send email with this email account using my Gmail application.

I'm going to load the PC version of TB and see if I can successfully set it up. Besides that I'm at wit's end. In the meantime I maintain access to my mail account via the provider's web access.

Thank you for the detail and description of symptoms. Oopps - edit for IMAP/POP, not SMTP ... Be aware that sending from webmail proves noting - when you use webmail you log in directly to the provider service, but Thunderbird has to access it through their IMAP/POP server. That means any problem with the provider's server, or authentication, or any misconfiguration of your Tbird settings that does not match their specific IMAP/POP requirements will prevent Tbird receiving from them. Hence, check with the provider to find out what your Tbird settings are supposed to be. IONOS seems to host in multiple countries, so you would need to know the right local server and ports for where you are. Sometimes the server may just be down or failing to respond, IONOS support may know. If you can confirm that part, probably someone else will need to help check Tbird error logs for more detail of what is preventing that connection.

Referring to your earlier response - you said you checked the SMTP settings and provided a link to Thunderbird SMTP setup - but those are for sending email. If your issue is that you cannot download incoming email - those settings require POP or IMAP server settings in Tbird to match the provider's server.

Back at you and again thank you for putting up with this old guy. I'm making progress! I think (bear with me) that what provided the "All of a sudden" aspect of this mess is that IONOS switched my account from POP to IMAP which might explain why my TB Port was unable to connect.

So I did two things. First I downloaded the PC version and let the auto config set up my account. It did and downloaded my mail. Next I executed a new instance of TB Portable and used the IMAP settings used in the PC Version and gratefully was able to connect and load my mail.

So where do I go from here?

I see two courses of action. One is to somehow change my server settings from POP to IMAP on the Portable app that I have used for well over 10 years and as such have my saved email in several folders under a topic system. The second option is to move the saved email and address books from the existing Portable app to the new portable app that I just set up on new IMAP settings.

So I'm open to your best advice and with that I will need guidance on how to accomplish your solution. That being, how to change the server settings on my existing TB Port or move my info to the new working TB Port. Again my gratitude!

First I am glad you have a good connection now. IONOS switched you to IMAP? Hmm. Does that means POP is no longer an option? I really recommend you read up on the difference between POP and IMAP. They work very differently. The basic idea is with POP email exists on the server until you download it, then it exists on your device in Thunderbird, and the server normally keeps a copy for a limited time before deleting it. With IMAP nothing really downloads - the typical setup shows you the headers of emails but goes back to fetch them from the server when you open/view/reply to a message. Folders are "synced" - changes in either the server (webmail) or TB make the same changes at the other end, deleting from one deletes from both and so on. You may also need to "subscribe" folders in TB to see sub-folders that exist on the server. The one exception is anything you put in Local Folders in TB is only on your Thunderbird device and not on the server. That's in a nutshell. I am really not sure what happens to all the saved emails you have in folders on your portable app. If you look at webmail, you'll get an idea how much of that would be available through IMAP. There is a way to copy messages from TB saved folders to new folders under the IMAP account that should upload the emails to the server if you wanted. Or keep them in the Local Folders area and not on the server. Either way, take a copy of the Thunderbird portable profile containing all those emails before you try anything! https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data - see backing up a profile. Regarding portable - I have not used it so I am not sure how it differs from the desktop version.

Well I am very much obliged for your explanation between POP vs. IMAP. It was both eye opening and discouraging. I was in hopes I was well on my way to an easy solution but seems I still face some road blocks. As mentioned apparently IONOS doesn't give me a choice as to using my existing POP settings which prevents a connection.

If I grasp what you provided it is not possible to mix my saved emails by importing them into the TB that has been set up on the IMAP scheme. I do see I am still able to set up folders in the new app and move emails out of my inbox as before. I have pretty much resigned to begin using the new app and saving any wanted email in folders as I have in the past. If I need to access an email from my old TB to simply open the app to view and if necessary forward it to my active TB. Thankfully I can still send email with the POP app setup.

You have been very helpful and I again thank you for sharing your knowledge but even more, for your patience. I can't say that the problem is completely solved but I am at least back up and running. Best regards!

It is possible to import and mix those saved emails, but needs to be done cautiously. Bear in mind - mixing them in with the IMAP folder structure mean uploading them to the server, rather than just moving them around in your own computer. The article on Profiles tells you more about how to move your existing profile and all the contents, including address book and saved emails to a new active TB. I suggest you start a new question asking how to keep emails from your old POP profile and transfer them and address book to a new TB Portable IMAP account. Best wishes!