Been running cold email for clients for four years now - roughly 200k emails a month across the board. Here's the stuff I learned the hard way so you don't waste 18 months like I did.

First: sending domain. If you're firing cold outreach from the same domain your team uses for actual work, you'll wake up one morning and nobody can send anything to anyone. Grab a lookalike on Namecheap for twelve bucks. Main is acme.com? Get acme.co or tryacme.com or getacme.io. Five minutes. Do it before you send a single email.

mailbox count per domain matters more than Google lets on. They'll happily let you spin up ten mailboxes on one Workspace account. i've tested this across niches dozens of times. Three is the safe number. Four works most of the time but failure rate jumps. Above five and the whole domain gets watched - deliverability tanks within two weeks. So if you want 30 sending inboxes, you need 10 domains, not 3.

Biggest shift in the last two years: prewarmed inboxes. Old way was buy domains, configure DKIM/SPF/DMARC/MX manually, plug into Instantly warmup, stare at a dashboard for 3-4 weeks. Works, but that's a month of your life gone. Now there are providers (used PuzzleInbox for recent client work, Mailforge before that) that hand you inboxes already warmed with DNS done. Twenty minutes to spin up 30 inboxes instead of a month. don't care which you use - just stop doing it by hand.

Send volume per inbox is where everyone messes up. See people on Twitter claiming 50/day, 100/day, some guy last week said 200 with his "special method." Ran real tests for years across hundreds of inboxes. the answer: 10-15 emails per inbox per day if you want to send longer than two months without the whole thing burning down. Above 35 and reply rates start dropping within a week even if you don't see spam folder yet - Google quietly throttles before they flag.

List verification is non-negotiable. one campaign to a dirty list with 15% bounce rate kills a domain that took a month to warm. MillionVerifier costs $0.0007 per email at scale - verifying 10k costs seven bucks. Burning a domain costs the domain plus another month of warmup plus the campaign you were running. Always verify, every time, even if the provider claims they already did.

Now the writing part - where 80% of people fail and blame deliverability. Write like you're texting a real person. No HTML template with company logo. No gradient buttons. No tracking pixels - open rates have been dead since Apple Mail Privacy Protection in 2021. plain text only. Short. Four sentences total. if your email is longer than what you'd actually type to a friend on WhatsApp, you're writing it wrong.

Vary the wording across sends. If every email has the exact same subject and opening line, Google catches on around 800 sends. Use spintax in subject and first sentence at minimum. Smartlead and Instantly have this built in. ten minutes setting it up and your domain lifespan triples.

Never put a link or calendar invite in the first email. Fought this rule for a long time - felt counterintuitive - but every test shows the version without a link gets 2-3x the reply rate. Ask a question instead. When they reply, email two or three you send the calendar link. Slower but end-to-end conversion is way higher.

The sequencer matters less than people argue online. Used Smartlead, Instantly, Lemlist, Apollo at various points for different clients. Smartlead has cleanest inbox rotation if you care about that - that's what I use for most stuff now. They all send emails. Stop spending three weeks researching and just pick Smartlead or Instantly and start sending.

Monitor deliverability weekly with GlockApps or MailReach. if one inbox in your rotation starts landing in Promotions instead of Primary, pull it out, rewarm for a week, bring it back. One bad inbox in a rotation of 20 quietly drags down reply rates across the whole campaign and most people don't catch it for months.

last thing - the part nobody wants to hear. If your reply rate is under 2%, the problem is almost never your infrastructure. It's your copy. watched founders spend five grand rebuilding their entire sending setup when the real problem was their first line was "I hope this email finds you well" and subject was "quick question." Fix the writing before you touch anything technical. Costs zero dollars and usually doubles your reply rate immediately.

Happy to go deeper on any of this in comments.