VPN to the rescue
When I want to send email from outside of Canada, the outgoing email is filed to Outgoing, the purgatory mailbox. It is never sent. The problem occurs whether I want to send email from my Android phone or my Windows laptop, using a desktop client like Eudora or eM Client, or mobile app, like AquaMail. Who blocks the email, and why, I don't know.
I asked my ISP's tech support. They had no clue, suggesting that I instead use their Webmail client, which is only slightly worse than Gmail's Web client. (The Webmail client is, admittedly, effective in overcoming geographic boundaries, but awkward to use.)
Fool 'em with VPNs
The solution is to use a VPN, a virtual private network, which fools everybody on the Internet and all software on your computer that you are in a different country. There are numerous VPNs that provide a basic service for free. I use TunnelBear, which offers 500MB a month of data transfer at no cost; paying for TunnelBear gets me unlimited data and use on up to five computers at once. (I use it at home on all our computers as a extra layer of protection.)
So, download and install a VPN like TunnelBear (https://www.tunnelbear.com/download), and then specify your home country, the one where your ISP is located. In my case, Canada. Problem solved.
If you have emails stuck in the Outgoing box, then you'll need to resend them. In some cases, the email client is smart enough to send them once it senses that you are "back in Canada." In other cases, you need to manually resend them, which might involve moving them to the Inbox, forwarding them as an original, or some other tactic.
I use TunnelBear to watch videos, such as live news events, that are geographically locked. Some jurisdictions, however, like China, and some software giants, like Netflix, block VPNs. So, there is an alternative.
The Alternative to VPNs
There is an alternative solution, involving a "visual" VPN like TeamViewer (https://www.teamviewer.com/en/download/windows). It displays on your local screen (laptop or Android device) what is displayed on the distant computer to which you connect. I primarily use this software to support the computers used by elderly relatives. It lets me see what is happening on their computer screens, operate the software, and even reboot their computers.
When I am abroad, I use TeamViewer to access my desktop computer back home. I've used it sometimes to transfer files that I forgot to take along, but mostly I use it to access my Eudora email client running on my primary desktop computer. I go through the incoming emails, answering them, and filing them into mailboxes.
It is possible to watch geographically-locked and VPN-blocked video with TeamViewer, but the frame rate is slow. It works, because as far as Netflix is concerned, the video is being watched on a geographically-correct computer. I don't know if TeamViewer is effective at evading the Great Red Firewall imposed by China.