One more thing to add. I did install Opera Mail and was able to send email out. So it appears that the problem is somewhere in the Thunderbird settings.

You should talk to your VPN provider which ports are allowed.

Outgoing server (SMTP) error. The server responded: Service not available

This may be a problem of your email provider's server, and not related to the VPN at all.

I tried to change ports as was suggested by Mozilla support to another user.

There is no point trying arbitrary settings. Use the server settings as per your email provider's instructions.

Another suggestion by the VPN support was to change to the IKEv2 protocol

I don't understand how that is related to Thunderbird.

1. The first VPN techsupport suggestion was to change the STMP server configuration from the insecure port 25 to ports 587 or 465. In fact, in my case the default configuration was to port 587. Anyway, neither 587 or 465 or 25 worked.

2. My usual email provider setup has been working perfectly well, except when VPN is used. The outgoing email doesn't go through only when I'm connected to a VPN server. This tells me that the problem is in how Thunderbird acts in the VPN environment. The fact that Opera Email doesn't have the same outgoing email problem with VPN also seems to point to the same.

3. I didn't try arbitrary settings, but only suggestions that VPN techsupport has offered.

4. The idea of IKEv2 again was something VPN suggested to address the email problem. I have no idea of their reasoning on how it may relate to Thunderbird.

Here is another alert when I attempted to send mail while connected to another VPN server:

An error occurred while sending mail: The mail server sent an incorrect greeting: Cannot connect to SMTP server 107.14.73.68 (107.14.73.68:25), connect error 10060.

That is because you didn't follow your email provider's instructions as advised earlier. Also as said before, check that the ports required as per your email provider's instructions are not blocked by your VPN provider.

I don't know what Opera Mail is doing to make it work. Presumably they do use some sort of proxy, which is allowed through the VPN. I'm guessing here though.

Are you saying that I should ask my email provider for instructions on how to configure my SMTP server in Thunderbird to let outgoing mail through when connected to a VPN server?

If that isn't what you're saying, I don't understand what it is.

I just spoke with my email provider (Spectrum) and they insisted that the problem must be with Thunderbird in the VPN environment. They asked me to send email via webmail and I had no problem. Spectrum techsupport further said that there are no filters or blocks on their end. So, at the end, they advised me to go back to you.

syusim said

I just spoke with my email provider (Spectrum) and they insisted that the problem must be with Thunderbird in the VPN environment. They asked me to send email via webmail and I had no problem. Spectrum techsupport further said that there are no filters or blocks on their end. So, at the end, they advised me to go back to you.

Of course they did. just ask them one question. Can you connect to the spectrum mail server if you log into the internet using another internet provider. I think the answer to that is no. And your VPN looks like you connected from somewhere other than their network so they don't let you log in.

Try using the settings they provide for mobile here https://www.spectrum.net/support/internet/email-mobile/

Maybe so. But don't you realize that I have no problem with receiving email, just with sending?

Matt, also, are you saying that if I duplicate the mobile device SMTP settings on SMTP settings of my desktop Thunderbird, the latter should work with VPN? If so, what should I select for Authentication method? I have no problem sending and receiving email on my smartphone, but I don't use VPN with it.

My guess is your smart phone is a bundle with your internet, so uses the same supplier. ipso facto no problem.

It has always been the SMTP server that comcast restricted I am assuming that continues. It is a great way to make doing thinks inconvenient so you buy more services from them without making reading your mail a problem.

IF you phone is not "bundled" you might want to look at what servers it is actually using to send mail! probably the ones I linked to earlier.

What are the default Thunderbird SMTP settings for: Port Connection security Authentication method

I've been changing these back and forth to see if any of them would work with VPN, and now I'm concerned that I've messed them up even for regular mail sending.

Here are the SMTP settins on my phone: POP3 server: mobile-smtp.roadrunner.com Security type : NONE Port: 587 Authentication required before sending emais: ON And I have no problem sending email from my phone, and that's without VPN.

lets see, Spectrum designate

For IMAP: mobile.charter.net: 993 For SMTP: mobile.charter.net: 587 SSL: This setting should be ON for both SMTP and IMAP.

Given the road runner and charter named servers are not routed to the same IP address, either might work for you. mobile.charter.net [68.114.188.72] whereas mobile-mtp.roadrunner.com redirects to cdptpa-twc-vip.email.rr.com [107.14.166.68]

I would suggest you check them without th VPN and confirm they work before you move to trying changing anything with it on.

You might also want to look at Options > Advanced> Network and disk space > Settings. It might be that changing the proxy to NO proxy might opt Thunderbird out of your VPN It should not work, given VPN and Proxy are different animals, but I vaguely remember something from a topic here years ago.

Does your VPN software offer an option to not route certain ports through the VPN? (Who is the VPN provider anyway?)

Here's a little update. The VPN in question is NordVPN.

I called Spectrum support again and we went over the SMTP settings. The only thing they suggested to change was name of the server. I've done that, even though I believed it had nothing to do with my problem. They told me once in the past that they have numerous servers under different names, and it makes no difference which one I choose. They did assure me again that they're not aware of any limitations on their end related to VPN, and sent me back to the VPN support.

Now, the very first NordVPN suggestion was to try a server other than they first recommended by default --the one in the US. Since then, I tried ones in Canada, Latvia, and South Africa, and none of them made any difference. But today, just for the hell of it, I decided to try one more. Just from the top of my head I settled on Mexico ... and guess what? The email went through. I went back to the US and Canada servers and the same old email problem happened again.

So, after all, could it be the culprit, and some VPN servers don't let email through and some do? Keep in mind, this is my one and only experience with VPN.

I guess I was happy prematurely. Several hours later whiile still connected to the same Mexico VPN server, the mail didn't work again.

I have recently starting using the NordVPN. At first, I had trouble sending mail using Thunderbird. I am a Spectrum user. Mine is the roadrunner.com. Others are xx.twc.com or simply twc.com. What I found was to go to Tools and then to the bottom of the Accounts Setting box that says Outgoing Server (SMTP). You may find a listing of several server names for TWC and they all said mail.twc.com for me. I edited the first one and changed it to smtp-server.roadrunner.com. Also I had to change the Connection Security to 'None' for it to work. I know, but if you are using a VPN, you have protection anyway. This is for username@roadrunner.com and I cannot verify any other usernames.

This is going to be interesting if it keeps working. Mine is username@maine.rr.com. My last conversation with Time Warner support they said to change both POP and SMTP servers to mail.twc.com. Now, following your suggestion, I changed my SMTP server to smtp-server.roadrunner.com and had no problem sending mail to myself. However, I had unsubscribed from NordVPN, so I can't test it at the moment. I just sent them email asking to reactivate my subscription for a few days to try what you suggested and am waiting for their response.

In my 20 or so days of trying to brainstorm it with NordVPN, one of their suggestions was to try one of their newest, higher numbered servers. And with one of them, the email did work for awhile. However, in 48 hours or so, it stopped working again. Now I have a long email from them with a couple of new ideas, but I had no chance to try them. I believe one of them is similar to what Cyberghost VPN offers, which is to set up email to bypass the VPN server and so being let through. Maybe that's the last resort, but I'm net ready to concede yet.

Please share your progress going forward.

With the changed SMTP server name, the two highest numbered US servers and the highest numbered German server passed. The UK and Swiss servers -failed.

OK Syusim, I see what you are saying and not all connections work. I was on US 1570 and tried US 1630 @ 6% and it failed. US 1455 @ 6% works fine. I am only sending email out from Thunderbird to my roadrunner.com accounts and to my gmail account. All should work. I will attempt to talk to NordVPN to see what they say why all locations don't work including foreign. I will advise. I definitely don't want to stop using VPN and I like Nord just fine. My junk mail has dropped drastically. I use to get 20-30 a day and now only 4-5. Thunderbird is not the only one to cause problem. I use Blue Iris Camera monitoring software from Perspective and I can no longer use the mobile version on android on a Galaxy S6 phone. The developer says he doesn't know anything about VPN and yet his software is extensive! Now that is weird and is he going to offer a solution? Remains to be seen! This involves my home security system with self-installed cameras.

Now I had the same US server refused my second outgoing email to pass through just 30 min after the first. I also send email to myself to try if it works. It's not good to have to leave the server when one needs to send email, even if it's on and off. NordVPN has had many suggestions which I tried, one after the other. They sent me a long email with new workarounds yesterday, and, if you like, I'll be happy to copy it to you.