A seed list, defined
The word comes from the planted address: an address you seed into a recipient list so that you, not only your customers, receive the campaign. A seed list is a set of them, spread across the providers your audience uses, each one reporting where the message arrived. The sending tool reports “delivered” when the receiving server accepted the message; it cannot see whether the provider then filed it in the inbox, the Promotions tab or spam. The seed can, because it is a mailbox at that provider looking at its own folders.
Three details separate a seed list from a handful of test addresses. It covers every provider that matters to the list, so a result is per provider rather than a single yes or no. It is inside the real send, so it measures the campaign as sent, with its content, its volume and its sending domain, not a test message sent on its own. And the mailboxes are real accounts with history, because a provider filters a brand-new mailbox's incoming mail differently from a mailbox it has watched for years.
What a seed list is for
- Placement per provider. The main use. A campaign that reaches 92% of the list at Gmail and 40% at Outlook has one problem, not a general one, and the fix is different. Google's and Microsoft's own dashboards (Postmaster Tools, SNDS) report reputation and complaint signals for the domain; neither reports where a given message landed.
- The Promotions question. At Gmail a message can be accepted, reach the inbox area and still be filed under Promotions. For a newsletter that may be fine; for a cold email it usually means unread. Only a seed at Gmail can tell the two apart, which is why the columns on a seed report are inbox, promotions and spam rather than inbox and spam.
- Drift over time. Placement moves as reputation moves. A seed list that sits in every send shows the week a provider started filing you to spam, which a one-off test taken a month earlier cannot.
- Seeing the email as received. Some teams also use seeds to open the campaign in real clients for rendering checks. That is a side use; a seed list that only renders is a QA tool, not a deliverability one.
Seed list vs warmup
The two are often confused because both involve mailboxes engaging with your mail. They act at different times on different things. Warming builds the sender: before and between campaigns, an AI persona on each of your mailboxes holds real two-way threads across the MailStrike network, so the sending domain accumulates the engagement history providers trust. Seeds protect the send: during a specific campaign, or just before it, real consumer mailboxes on the receiving side report where the campaign landed and, with MailStrike's seeds, act on it.
- When it acts: warming runs continuously on a ramp; a seed list acts on one send.
- What engages: warming is your mailbox in conversation with the network; seeds are recipients receiving your campaign.
- What it produces: warming produces reputation; a seed list produces a placement result per provider and, for active seeds, engagement signals on that campaign's content and domain.
- Who it is for: warming, any sender; seed lists, B2C senders reaching consumer Gmail and Outlook, where MailStrike's seeds live.
A B2C sender with a spam problem usually needs both: seeds to protect the campaigns going out now, and warming to rebuild the reputation that put them in spam. A B2B sender reaching Google Workspace and Microsoft 365 mailboxes is in warming's territory; seeds cover consumer providers only.
Aged seed accounts vs fresh ones
A seed is only as good as the provider's view of it. A consumer mailbox created last month has no reading history, no contacts and no pattern of what its owner keeps or reports, so the provider has little to go on when it files mail for it, and it treats new accounts cautiously in other ways as well. A mailbox that has been read daily for years is the recipient your real customers resemble. That is why the mailboxes behind MailStrike's seeds are real, aged consumer accounts at Gmail and Outlook rather than accounts created for the purpose, and why a seed list you build yourself from fresh signups tends to show a placement picture your customers do not see.
How much placement actually differs between older and newer seed accounts on the same message is a measurement MailStrike is running across its network. The number is not on this page until it exists; when it does, it will be here with its sample size.
What MailStrike's seeds do beyond reporting
Most seed lists observe. MailStrike's seeds correct. The seeds are exported in batches into your recipient list; you send the campaign as usual; then, at each seed mailbox, the seed engages with the message the way an interested recipient would:
- 1
Open and read
The seed opens the message and stays on it for a while, with dwell times that vary from seed to seed rather than a single fixed pause.
- 2
Rescue from spam and Promotions
When the message landed in spam, the seed moves it to the inbox and marks it not spam; when Gmail filed it under Promotions, the seed moves it to the primary inbox. Both directly contradict the provider's verdict on that message.
- 3
Mark important
A small share of the seeds mark the message important, a positive signal the provider records against the sending domain.
- 4
Report
Every seed reports where the message first landed, so you get the placement result per provider for the campaign as sent, alongside what the seeds did about it.
Two ways to use one: mix-in and pre-send
Mix-in. The seeds are mixed into a real mass send. As the campaign goes out, they land beside your customers' copies and act on whatever they find, so a send that starts drifting toward spam at one provider gets engagement signals on that provider while the campaign is still in flight. The use is protection: a large send should not be able to damage the domain unwatched.
Pre-send. The campaign goes to the seeds first, before the real list. The seeds open, rescue and mark, which builds engagement signals on that content and that domain at each provider ahead of the real send. The use is preparation: the same message then reaches your customers with a record behind it rather than as an unknown.
Most B2C teams use both: pre-send for the campaigns that matter most, mix-in on everything.
Setting up a seed list
- Export the seeds as a CSV into whichever tool sends your campaigns, and put them on their own segment so their opens stay out of your campaign metrics.
- Publish one DNS TXT record to verify the sending domain. Nothing else in the sending stack changes; the campaign is sent exactly as before.
- Send, then read the report: inbox, promotions or spam per provider, and what the seeds did.
MailStrike's Seed Lists are a standalone product priced by seed volume; a warming plan is not required, and they cover consumer Gmail and Outlook.
Reading a seed report against the benchmark
A seed report is three columns per provider. The inbox column is the share of seeds at that provider that found the message in the primary inbox; Promotions is Gmail's marketing tab; spam is the junk folder. Read the numbers against the row of the placement test that matches your sender type and domain age, because a newsletter from an established domain and a cold email from a three-week-old one have different normal results at the same provider.
Two readings to keep apart. A high Promotions share with a low spam share is a classification problem: Gmail accepted the sender and sorted the content. A high spam share is a reputation or authentication problem, and the fix starts with the domain rather than the copy: check it with the reputation checker, then warm.