Email not working for two of our members - error message

I'm trying to send an email (as I always do) using the mail button in the agenda.
I know the emails are going out because I sent a test message and people wrote me back immediately.
However, I receive this error when sending.

The following members have disabled agenda emails
in their member profiles and were skipped:
Michelle Dettlaff
DTM (invalid/non-working email address),Paul D. Dettlaff, DTM (invalid/non-working email address)

The funny thing is I am michelle@design4dot.com. I have a secondary email (my gmail account) and it works for that.
Paul is my husband. Is it my domain name? I'm not sure how to troubleshoot this? I did a search for the error and nothing else came up.

Thank you.
Michelle Dettlaff
6193.toastmastersclubs.org/

Your website is hosted in a datacenter that continuously spams our servers and was blocked. I have unblocked your mail server for now.

I'm with Host GAtor. Can I address this with them?
Any suggestions?
Thanks
M

no they can't control their multitude of spam clients.

Hi Brian,

I think I'm running into an issue again with sending emails to members-6193@toastmastersclubs.org
I"m getting a kickback message

This is the message.
This is the mail system at host gateway31.websitewelcome.com.

I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can delete your own text from the attached returned message.

The mail system

<members-6193@toastmastersclubs.org>: connect to
mail.toastmastersclubs.org[50.19.253.65]:25: Connection timed out

Should I be calling my hosting company?
Thank you.
Michelle

Michelle, which recipient (need the email address)?