"The only change in my recent email activity is that for the past 10 days I have been writing kind of a diary email to all my friends and family (about 70 recipients). The frustrating part is that they write to me and I can't reply to them!
"If you have any advice and time to give it, that would be really really nice."
(Thursday, April 9, 2020 Edit: Updated title to better reflect the likely underlying issue.)
Thierry, thanks for reaching out. First thing's first: Do you actually have your own email server? You mentioned "MTA issues" in your original email to me. But you mentioned using mail.com, a free webmail provider. If you do own your own email server, you should be sending as your own domain name, and not using the domain name of a free webmail provider. In this world of email authentication and DMARC restrictions, you'd be sending unauthenticated mail and your ability to get mail delivered successfully is going to suffer.
But, assuming you do NOT have your own email server -- if you are just a customer of mail.com -- then you aren't really in a position to troubleshoot and fix these deliverability issues. You're basically just a customer of a provider with shared infrastructure, and it's really up to that provider to have to fix those issues. If you want to proceed as is, you'd really need to reach out to them and ask them to fix whatever the Spamhaus issue is here. (I did a bit of searching and couldn't find any obvious Spamhaus issue, so I'm not really able to advise on that directly.)
Since you want to send to a group of people, maybe it's time for you to look for a tool that will be more directly suited to what you want to do. If you're a representative of a qualifying organization, iContact has some free tools you might want to consider.
Yahoo Groups and Google Groups are free community/discussion group services that could easily handle what you're doing.
Or, if you want to investigate the option of using a free or low cost broadcast/newsletter email service, friends suggest checking out any of these: Mailchimp, MailerLite, SendInBlue, Klaviyo, MooSend, MailJet, ConvertKit, or Omnisend. I haven't tried any of these but friends tell me they might fit the bill here. SendInBlue, for example, has a free tier that allows you to send 300 emails a day.
If you're looking to set up a for-pay newsletter, I've seen friends use Substack to do this. One friend uses this to publish a newsletter where you can pay to get every weekly edition, or get every monthly edition for free.
If anybody has an experience with these free or low-cost ESP platforms, feel free to share them in comments, and let's see if it can help guide Thierry in right direction.