Deliverability basics: warm-up, bounces and suppression
Last updated 1 August 2026
Deliverability is the difference between an email being sent and an email being read. Most of it is handled for you, but it helps to know what is happening and why some sends are deliberately slowed down.
Warm-up ramps
A brand-new sending domain with no history that suddenly sends 50,000 emails looks exactly like a compromised account, and providers treat it accordingly. Solstral therefore gives new domains a modest daily budget that increases on a schedule as the domain establishes a reputation.
The important detail: campaign recipients over the day's budget are deferred, never dropped. They stay queued and go out as the ramp allows. A campaign that looks like it is sending slowly during warm-up is working correctly.
Bounces and complaints
A hard bounce means the address does not exist. A complaint means someone marked your message as spam. Both are recorded within seconds of the provider telling us, and both suppress that address across the whole platform.
Continuing to mail addresses that bounce is one of the fastest ways to damage a sending reputation, which is why this suppression is not optional and not something an individual campaign can override.
Suppression is checked three times
Every marketing send is filtered against the suppression list at three separate points: when the audience is resolved, again at the moment each individual message is about to be sent, and continuously afterwards as tracking events arrive. Three independent chances to catch a bad address means you cannot accidentally email someone who unsubscribed, bounced or complained.
Unsubscribes
Every marketing email carries an unsubscribe link, plus the one-click headers that Gmail and Yahoo now require for bulk senders. Unsubscribing updates all of that address's list memberships at once — not just the list the campaign happened to use — and adds a marketing suppression.
That suppression is reversible through the preference centre if the person chooses to re-subscribe later. A block created by a bounce or a spam complaint is not, because those are signals from the provider rather than a preference of the recipient.
What you still need to do
Send to people who asked to hear from you, remove addresses you bought or scraped, keep your sending domain aligned with your link domain, and give recipients an obvious reason to open. No platform can fix a list that should not have been mailed.