IP warm-up
Building a sending reputation gradually, and what changes when you send from shared infrastructure instead
IP warm-up is the practice of increasing volume from a new sending IP gradually — starting with a few hundred messages a day to your most engaged recipients, and roughly doubling over a period of weeks — so that mailbox providers build a positive record before they see real volume.
The reason it exists is that a brand-new IP has no reputation, and no reputation is treated as suspicious rather than neutral. A new IP that sends a million messages on its first day is behaving exactly like a compromised one.
When it applies to you
Only when you have a dedicated IP. On shared infrastructure, the reputation of the IPs already exists and is maintained by the provider across all of its senders, so there is no IP to warm.
What still applies on shared infrastructure is domain reputation, which is yours and travels with you. A domain that has never sent has the same problem an IP does, and the same answer: start with the people most likely to engage, and increase over weeks.
In Sendly
Sendly sends over shared, actively monitored infrastructure, with per-project sending limits on top. There is no self-serve dedicated IP with a warm-up schedule you control today; if that is a requirement, it is a conversation to have before you migrate rather than after.
The per-project limits mean a first campaign of unusual size may be paced rather than released at once. That is protective, not a fault, and it is another reason to tell us before you move volume across.