I am a Lemlist user. I was looking for a similar tool to test new campaigns, with new domain names, if possible an LTD.

And here is MailRush.

The first step is to configure DNS. It's classic, but I needed the support. My domain was hosted and had MXs, I was missing some information (set existing MX priority from 0 to 1).
I had Jorge's help on Saturday night here (Europe), it's really great not having to wait for hours.
I like the user interface, everything is clear and simplified.
Great features.
I read some reviews about the limits of the deal. For me they are totally justified.
MailRush wants to avoid spammers, or errors which can be seen as spam and harm all users.
Cold emailing is a craft, not an industry.

Eight custom fields with content spinning are there to personalize the templates.
You can prepare everything in Excel and import the fields.
It's possible to manage several domains (one domain = one code) in the same account, therefore without stacking.
I will also buy codes with different emails to manage them with VAs or clients.

A deal not to be missed, whether you are already experienced in cold emailing or if you are planning to start.