Email Issues

(Having issues with my email, and a search of the posts here didn't seem to have anything that suggested a solution I could implement. I've tried having one of our officers with access try to whitelist, and that didn't help.)
Up until about two weeks ago I had no issues with my email address, and now I cannot send emails to my club from Outlook. I thought it might be an issue with a new installation of Outlook (I tried on my old computer, and my phone--all Outlook), but I'm not sure because I sent from another email address and that went through, although flagged as spam. I can still email from the web client provided by Free Toast Host, which I have been doing, however, I did get a pop-up (once) that warned me that mine and my husband's emails would not be included in the recipients list as they were bad email addresses. So, I'm stymied. Below is the return info from one of the non-deliverable emails, and the delay info as well. Our email addresses are christien@hossingaround.com and bryan@hossingaround.com

THANK YOU FOR THE FREE SITE AND ESPECIALLY FOR THE HELP!
-Christien Sweeney
At Ease Toastmasters, Georgetown, TX
#5963837

Reporting-MTA: dns; server54.web-hosting.com

Action: failed
Final-Recipient: rfc822;vpe-5963837@toastmastersclubs.org
Status: 5.0.0

Reporting-MTA: dns; server54.web-hosting.com

Action: delayed
Final-Recipient: rfc822;members-5963837@toastmastersclubs.org
Status: 4.0.0

You host your website in a data center that frequently spams the FTH server and your email IP was blocked.
I have unblocked the IP.

Thanks so much for such a quick fix and reply.

Is there anything I can do to prevent future incursions? (I mean other than changing website host)

You use a cheap hosting service you get what you pay for.