Execution and sending
Behavior Reviewed · not yet fact-checked
In short
How does Reply select a sending mailbox?
Reply assigns each new contact to one of up to 100 sequence email accounts using round-robin logic, from any source. All follow-ups send from the same account as the first email unless that account is removed. Matching email providers, when enabled, pairs contacts with same-provider senders; the Reassign email accounts setting redistributes contacts automatically.
At a glance
| Aspect | Detail |
|---|---|
| What it governs | Which of a sequence's email accounts is assigned to each contact, and which account each email sends from |
| Trigger | A contact is added to a sequence with connected email accounts (manually, via CSV, API, or integrations) |
| Inputs | Email accounts added to the sequence, contact's detected email provider, Matching email providers toggle, Reassign email accounts setting |
| Result | The contact gets a sending email account; the first email and all follow-ups go from it, in one thread |
| Configurable | Sequence email accounts, Matching email providers (per sequence), Reassign email accounts (account-level setting) |
| Does not | Decide when the send happens — that is When Reply sends — or reassign contacts already assigned to an active account |
| Plans | Adding teammates' email accounts to one sequence requires Team Edition |
Rule summary
A sequence can send from up to 100 email accounts. New contacts — added manually, via CSV, API, or integrations — are assigned to the connected accounts one by one using round-robin logic: the first contact to the first account, the second to the second, and so on, cycling back to the first. If the sequence has multiple email steps, all follow-up emails for a contact are sent from the same email account as the first email, unless that account is removed from the sequence.
Trigger
A contact is added to a sequence that has one or more email accounts connected, or the sequence's email accounts change (an account is added or removed).
Decision logic
- When a new contact enters the sequence, Reply picks the next email account in round-robin order, spreading sending evenly across all connected accounts.
- If the Matching email providers toggle is on for the sequence, Reply first pairs the contact with a sending account whose email provider matches the contact's (Outlook to Outlook, Gmail to Gmail). Unmatched contacts are distributed among the available accounts using round-robin logic.
- The assigned account sends the contact's first email, and every follow-up sends from that same account — the conversation stays in one thread.
- If the contact's account is removed from the sequence, follow-ups send from the account the contact is reassigned to, still in the same email thread.
Assignment when accounts change:
| Action | Condition | Assignment behavior |
|---|---|---|
| Connect a new email account | No other account connected, or contacts have never had accounts assigned | Reply assigns the new sending email automatically |
| Connect a new email account | Active accounts exist and contacts are assigned to them | Nothing changes for assigned contacts; newly added contacts are assigned across all accounts, including the new one |
| Upload contacts to a sequence | One or more accounts connected | New contacts are assigned automatically across all connected accounts |
Result
Each contact shows a sending email account (the Sending email column in the People tab). The first-step email and all follow-ups for that contact go out from it.
State changes
| Field | Change |
|---|---|
| Contact's sending email | Set on assignment; changes only on removal, reassignment, or a manual change |
| Email thread | Preserved — even after switching accounts, new emails arrive in the same thread |
| Sequence toggle | An error notification appears over the toggle when contacts are left unassigned |
Exceptions
- Removing an account leaves its contacts unassigned — you must assign them manually (filter People by Unassigned, then link a sending email) unless the Reassign email accounts setting is enabled.
- Manual assignment is also needed when you add a new account to replace a deleted one, or when contacts are already assigned to existing accounts and you expect them to move — Reply does not change existing assignments automatically.
- Provider detection happens only in sequences — a contact merely uploaded to Reply but not added to a sequence gets no provider detection; undetected providers show as
Unknown. - Toggling Matching email providers on or off does not touch existing assignments — only newly added contacts follow the new logic.
- Teammate signatures — if a removed account's contacts are reassigned to a teammate's account with a different signature, update the follow-up templates so the thread reads consistently.
Configuration that changes this rule
Matching email providers (Sequence > Settings > General settings, off by default) switches assignment from pure round-robin to provider-matched first. Reassign email accounts (Settings > Emails > Sequence email accounts) changes removal behavior: only contacts without a sending account are auto-assigned, contacts added before any account was connected get assigned once mailboxes are added, and contacts of a removed account are redistributed among the remaining accounts without touching other assignments. You can also change a contact's sending email manually from the sequence People tab — sequence owners only, and the new account must already be in the sequence's Settings tab. Also raise Max new daily contacts and Max number of emails per day to match the number of accounts added — see Configure sending limits.
Limits
| Limit | Value |
|---|---|
| Email accounts per sequence | Up to 100 |
| Assignment order | Round-robin, one contact per account in turn |
| Follow-up account | Same as the first email's account, unless that account is removed |
| Who can change a contact's sending email | Sequence owners only |
FAQ
Does a contact always hear from the same mailbox?
Yes — all follow-ups send from the same account as the first email. The only exception is removing that account from the sequence: the contact's follow-ups then send from the reassigned account, still in the same thread. See Email accounts.
Why are contacts not assigned to my email?
Three common causes: an active sending email was deleted (its contacts are not reassigned automatically), a new account was added to replace a deleted one, or a new mailbox was added while contacts were already assigned to existing ones. Filter the sequence People tab for Unassigned contacts and link a sending email, or enable Reassign email accounts. See Why is a campaign not running?.
What happens if I switch Matching email providers mid-sequence?
Nothing for contacts already assigned — the toggle affects only newly added contacts. Matched contacts get a same-provider sender; unmatched ones fall back to round-robin.
Can I send one sequence from my teammates' mailboxes?
Yes — with Team Edition enabled you can add both your own and teammates' email accounts to the same sequence.
Related
Build with Reply
- REST API: docs.reply.io — sequence account assignment endpoints
- MCP: agents.reply.io/mcp — agents assign accounts to sequences