My emails land in spam

Check your email setup. In Settings → Mailboxes press Check email setup. It checks SPF, DKIM and DMARC, the three records that prove your emails really come from you. Add any missing ones at your domain provider.
Use a separate domain for cold email, never your main one, so your everyday email stays safe.
Let new mailboxes warm up. Don’t skip the slow start on a new mailbox.
Keep volume per mailbox low. Add mailboxes instead of raising one mailbox’s limit.
Watch bounces. If a mailbox pauses itself, check where those addresses came from before resuming.