Email Deliverability - Best practices? (I killed a domain)

Hi Searchers,

Our firm is depending on a proprietary pipeline, to find acquisition targets, that is driven by email marketing. This morning I woke up to see a domain of mine was given a death sentence, resulting in every outbound email bouncing due to "Access denied, bad outbound sender AS(42004)". Fortunately, this was not my primary domain.

I had warmed up the domain through an email warmer tool, set up authentication protocols in the DNS such as SPF, DKIM, and DMARC, used plain text email formats, and abided by the general email marketing rules such as no link tracking. The emails were customized with company names, company city, industry, year founded, and years in business, and kept to less than five sentences.

I am not sure what resulted in my domain going to the guillotine, but my hypothesis is that this email was not warmed up appropriately as I had only used the warmer for a month and kept it at 30 emails a day... and then proceeded to try 100 emails in a day, resulting in "unusual activity".

If anybody has any input on my practices here, I would love to hear it. This has put a halt to my marketing and, to prevent this from happening again, I am warming up an additional four domains with 100 emails a day.

Thanks for reading.