Too many simultaneous connections — IMAP connection limit reached
Transient infrastructure, not a real failure
This IMAP error means the mailbox already has as many open connections as the server allows, so a new one was refused. It is transient infrastructure behaviour rather than a credential or delivery problem - Gmail permits roughly 15 simultaneous IMAP connections per account, shared across every client and tool.
What the server actually says
imap_auth_failed | Too many simultaneous connections. (Failure)What you see
Intermittent connection failures that clear on their own, often while several tools poll the same mailbox. Can masquerade as an authentication failure because some clients set an auth-failed flag alongside it.
Why it happens
- Several tools - sequencer, warmup, CRM sync, a desktop client, a phone - all holding IMAP connections to one mailbox.
- Connections not being released, so the pool leaks until it is exhausted.
- Polling too frequently, opening a new connection before the previous closed.
How to fix it
- Count what is connected to the mailbox. Every client counts, including phones and desktop mail apps. The limit is per account, not per application.
- Reuse connections instead of opening per operation. A pooled, reused connection avoids the churn that exhausts the limit.
- Back off and retry. It is transient - a short wait usually clears it with no intervention.
- Do not record it as a send failure. No send was attempted. Logging it as a mailbox failure pollutes health metrics and can trip auto-stop logic that watches failure counts.
What not to do
- Do not treat it as an authentication failure. Some IMAP clients set authenticationFailed alongside this message, which makes it look like bad credentials - reconnecting or rotating a working password wastes time and can lock the account.
- Do not retry immediately in a tight loop. That keeps the pool exhausted and prolongs the condition.
- Do not count it toward mailbox health. It is infrastructure, not sender behaviour.
Frequently asked questions
How many IMAP connections does Gmail allow?
Around 15 simultaneous connections per account, shared across every client. Tools polling frequently can exhaust that on their own.
Why does it look like an auth error?
Some IMAP libraries set an authentication-failed flag whenever the session fails to establish, including when the cause is the connection limit. Checking the message text rather than the flag is what distinguishes them.
How MailPilot helps
MailPilot classifies this error automatically on every connected mailbox and tells you which side is at fault, so a throttle is never mistaken for a dead recipient and a credential failure never suppresses a healthy address. It also monitors real inbox placement and checks SPF, DKIM and DMARC on every mailbox, which is where most policy rejections start.
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Last reviewed 2026-10-11 by the MailPilot team.