Cold email marketing campaign tools/set up

Hi all!

I'm fairly new to this cold emailing approach so hoping to get your views on a set up I have in place that's creating more issues than progress.

I've got a number of email domain set up through IONOS(I really don't like them so far). SPF added, DMARC added. DKIM not supported.
- 4 SMTP (3-4 weeks old)
- 1 SMTP (>1 year old)
- 2 EXCHANGE 2019 (1>year old)
- 10 EXCHANGE 2019 (3-4 weeks old)

I have checked both IP and domain for blacklisting and they seem to be fine.

I have an account with SalesHandy for the email campaign and they are fairly ok I would say. They definitely have a lot of interesting features and based on their algorithm my campaign is getting 75/100 quality wise.

I have a list of aprox 2000 subscribers, all checked email addresses, most are good, some are risky(according to the SalesHandy check).

Unfortunately I do encounter some issues.
- many of the emails do not reach the recipients(inbox or spam) and just go missing. I've been getting a lot of reports from old contacts that I have worked with in the past that they are not getting our emails anymore.
- some of the new EXCHANGE 2019 get disconnected from the campaign as soon as I add them without sending any emails

Any pointers would be definitely appreciated.