Cold email is judged by the receiving servers. These tools keep your domains out of spam folders.
Limits and hours
A hundred emails a day from one address leads straight to spam lists. Spread a campaign over several mailboxes, keep Emails per day modest, and send in working hours. See Campaigns.
Mailbox warm-up
A new mailbox that suddenly sends a lot looks suspicious. Warm up this mailbox, under Settings → Mailboxes, exchanges a growing number of emails between your own mailboxes for a couple of weeks: they arrive, get handled, get replies, and are pulled out of spam when they land there. Set the target Emails per day; the mailbox shows what it sent in the last two weeks.
The stop list
Nobody on the stop list is written to, from any campaign. People who unsubscribe, addresses that do not exist and people who complain or ask to stop get there by themselves. Add addresses takes addresses and whole domains as @firm.com.
Bounces
A bounce from an address that does not exist puts the address on the stop list. When too many of the last thirty emails bounce, the campaign pauses itself, by the Stop, % you set.
Unsubscribe
Keep {{unsubscribe}} in the footer. A person who follows it is never written to again, and the unsubscribe header lets their mail program show its own button.
Your domain
Before you start, check the sending domains under Deliverability: records, blocklists and inbox placement. See Domain records.