Where the defaults come from
40 cold emails per inbox per day is the ceiling most deliverability teams run at in 2026 on Google Workspace and Microsoft 365 inboxes, with warmup still active. Three inboxes per domain keeps a single bad day from burning more than three mailboxes of reputation. Both numbers are editable because aged domains with clean history can go higher.
Why not use the main domain
If cold email damages a domain's reputation, you want that domain to be disposable. Your main domain carries invoices, support and password resets. Keep it out of cold outreach entirely. The planner names sending domains after your brand so prospects still recognise you.
The ramp
New inboxes start at 10 a day and reach full volume over the warmup weeks you set. Keep automated warmup replies running throughout. Watch two numbers: bounces under 2% and spam complaints under 0.1%. Either one rising is the signal to stop and fix the list.
Questions
How many cold emails can one inbox send per day?
40 is the safe ceiling on Google Workspace or Microsoft 365 with warmup running. Some teams push to 50 on aged domains. Above that, placement drops.
How many inboxes per domain?
Three. It limits the damage if a domain gets flagged and keeps per-domain volume natural.
How long should warmup take?
Two to three weeks for a new domain before full cold volume. Keep warmup running after that, at a lower rate.
Should cold email come from my main domain?
No. Use separate sending domains that reference your brand, and keep the main domain for transactional and customer email.