Gmail has increased its security on incoming mail. Gmail sees your your sending domain name and the domain of the email host as being different and rejects the mail. Your email provider needs to make security adjustments to their server. This is not something you can do. This is not uncommon where an individual pays for a web host for a private domain. The best you can do is to check that you are authenticating on the SMTP settings.

Thanks for the quick reply! I am trying to locate where my SMTP settings is. I found on "Outgoing Server (SMTP)" under "Authentication Method" I have "Password, transmitted insecurely" checked. Should I change that?

Yes. Also check that you are using you have ssl/tls or starttls for connection security.

I will check SSl/TLS. If I should change my SMTP from "Password, transmitted insecurely," what should I change to?" The other options are:

No Authentication Encrypted Password Kerberos / GSSAPI NTLM

Under "SMTP Server" for "Connection security" the "None" box is checked. The other options are STARTTLS or SSL/TLS. Which would do you think I should go with?

It may not be useful, but knowing your email host name, such as AOL, verizon, comcast, etc., may be helpful

host name which I use for work which I am having issues is mail.cypressop.com

It appears this is your place of employment, but the email provider may be tucows.com. I suggest you check with employer on proper settings . You could experiment and try combinations of ssl/tls with ports 465 and 587. That's four possibilities and one may work.. However, I encourage you to alert your employer as what you are experiencing may apply to the others.

Thanks for all your help. Port currently is 587. Will take a screen shot of current settings and then try the 4 different possibilities to see if that helps. Where I work we don't have an IT department so nobody knows what to do! lol. We reached out to a local IT guy who goes around helping different companies and this is what he said.

"This is not a Thunderbird issue - it has to do with your current email provider and your domain name / DNS setup with cypressop.com.

All the major email providers (Google and Microsoft and others) have started to tighten the nuts and bolts down even further in the wake of the spam and scams.

To be honest, I tried to discuss this with Ben a few years ago, but he didn't want to listen. I'll be glad to sit down with y'all again and discuss it further."

IT guy always tries to get us to stop using Thunderbird. :)

I agree with that IT guy, that you do need to contact the email provider for the fix you need. They are also the ones to verify email settings . Someone in your company has contacts with tucows.com and they should notify them.

Thanks!! Last question I promise. You mentioned that I should change my SMTP settings to make sure I am Authenticating. Currently it's set at "Password, transmitted insecurely."

What would you recommend changing too? The other options are:

No Authentication Encrypted Password Kerberos / GSSAPI NTLM

I do not know, although some others here might. However, you have a corporate issue and I encourage you to escalate it appropriately.