Rolling out an AI SDR: volume, domains and deliverability

What the mailbox providers ask

Google, Yahoo and Microsoft publish what they ask of senders, and they ask more of bulk senders.

A cold message goes to someone who didn’t sign up, so every spam report it earns counts against the sending domain, at any volume. Write only to people with a real reason to hear from you (part 5 writes down who). Give every message a one-click unsubscribe, since Google notes that unwanted messages without one are more likely to be reported as spam, and honour each unsubscribe within 48 hours (part 8 sets out the rule).

Your main domain or a separate one

In February 2026, someone starting cold email for a small SaaS business asked on Hacker News whether to send 30 to 50 a day from the main product domain or a separate outreach domain; two AI assistants had given opposite answers. The providers’ rules don’t decide it, but they show what each choice carries.

On your main domain or a subdomain of it, the AI SDR’s mail joins one count with your product and marketing mail: Google’s own example adds 2,500 messages from a domain to 2,500 from its promotions subdomain and calls the sender bulk. On the main domain itself, its spam reports can lower the reputation of a domain that may also carry your invoices and password resets; one reply to the question says cold mail “hurt the deliverability of our transactional emails”. Yahoo asks senders to keep types of mail apart, by IP or DKIM domain: “Sending unsolicited commercial email can negatively affect your reputation.”

A separate domain has its own count, and Gmail tracks feedback per domain, so it builds its own reputation. But it starts with no history, needs its own SPF, DKIM and DMARC, and answers to the same rules.

A ramp with gates

Each mailbox has a ceiling. A Google Workspace user can send 2,000 messages a day, to at most 2,000 outside addresses (500 of each on a trial account), counted over a rolling 24 hours. A Microsoft 365 mailbox can send to 10,000 recipients a day and 30 messages a minute. These are the most a mailbox may send, not a pace to aim for. The 30 a day per inbox in Instantly’s guide is Instantly’s own convention.

Google’s guidance: “Start with a low sending volume to engaged users, and slowly increase the volume over time.” For an AI SDR, start with the contacts who have the strongest reason to hear from you. Google warns that suddenly doubling your volume can bring rate limits or a drop in reputation; if mail starts bouncing or being deferred, it says to reduce volume until the errors fall. Write the ramp and its gates down before the first send, and change one thing at a time, as in support part 11: more volume, a new mailbox or a new segment, one per week.

Count these yourself from day one. Postmaster Tools’ dashboards “might not include all data on days when your outgoing email volume is low”, and their spam rate covers only DKIM-signed mail that reached a personal Gmail inbox, leaving out company inboxes on Google Workspace. Take bounces and deferrals from your sending tool, count unsubscribes and replies asking you not to write again, and enrol your DKIM domain in Yahoo’s Complaint Feedback Loop, which sends you a copy of each spam report from Yahoo users. Leave opens out: “Google doesn’t track open rates.” Part 12 shows how to count it all.

When a gate fails, go back a step and find the cause before climbing again. If Gmail answers 4.7.28, you went over its quota: Google’s page says to send nothing for at least 10 minutes. Outlook’s 5.7.515 means the domain failed authentication, so fix SPF, DKIM or DMARC first.

Next in this series

Part 12: measuring an AI SDR. See all 13 parts.

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