Email Sending Limits

Kapsule applies sending caps to every mailbox so that one compromised account or one runaway script cannot damage the sending reputation that everybody else's mail depends on.

The caps are deliberately generous for ordinary business correspondence and deliberately tight for anything that looks like a bulk campaign. If you are writing to customers, suppliers and colleagues all day, you will never notice them. If you are trying to send a newsletter through a mailbox, you will hit them immediately, and this article explains what to do instead.

The Limits

Both counters are rolling windows rather than clock-hour or midnight-to-midnight buckets. When a counter is full, further messages are refused until enough time has passed for it to come back down. Nothing is lost permanently: wait for the window to roll over and send again.

The same two limits are applied twice over: once against the mailbox you authenticate as when you submit a message, and once against the address in the envelope sender of the mail we then relay out. That matters in one practical case. Sending under a different From address from the same mailbox, using an alias or a shared address, does not give you a second allowance.

Why the Caps Exist

Outbound mail from a shared platform is only as trusted as its worst sender. When one address on the platform starts blasting, receiving providers do not carefully separate that traffic from everybody else's: they downgrade the sending infrastructure. Caps are the difference between a bad hour for one account and a bad week for every customer.

The caps also work in your favour when something goes wrong on your side. A contact form with a broken loop, a plugin that retries forever, or a mailbox whose password has leaked will all stop at 100 messages instead of sending 40,000 before anyone notices.

What Counts Against the Limit

Every message you submit through the mail server counts, whichever way you submit it:

• Mail sent from webmail
• Mail sent from a desktop or mobile client over SMTP, covered in Setting Up an Email Client
• Mail sent by an application or website that authenticates as the mailbox

Mail that fans out consumes the allowance much faster than one-to-one correspondence, because a single message addressed to a large group becomes a delivery for each recipient. Sending to a 200-member mailing list is not comparable to sending 200 individual replies over a working day. Plan for that before you press send.

The Right Tool for Bulk Mail

If you need to reach a large audience, use a dedicated sending service and authorise it properly on your domain:

1. Choose a bulk sending provider.
2. Add their sending hosts to your domain's SPF record. A domain is allowed exactly one SPF record, so their hosts belong inside your existing one, not in a second record.
3. Publish their DKIM key on your domain as they instruct.
4. Keep your Kapsule mailboxes for correspondence.

Your domain then authenticates both streams correctly and one cannot damage the other. SPF, DKIM and DMARC Explained covers what each record does, and the Deliverability tab on any mailbox shows you what is currently published.

Other Limits Worth Knowing

These are not sending limits, but they are the other numbers people run into in the Email console:

Inbound Filtering Thresholds

Sending limits govern what leaves. Incoming mail is scored separately, and the thresholds are worth knowing because they explain where a message ended up:

• A message scored at or above the spam threshold is marked as junk and filed in the Junk folder rather than deleted.
• Only egregiously scored mail is refused outright at the point of delivery, which means the sender gets a bounce and knows it did not arrive.
• Nothing is silently discarded. Kapsule does not run a "delete it quietly" tier, because mail that vanishes without either party knowing is worse than mail that bounces.

You can override the scoring per mailbox with allow and block rules on the Spam filter tab. An allowed sender always reaches the inbox; a blocked one is rejected.

If You Need a Higher Limit

Genuine business cases exist: a booking system that confirms hundreds of appointments a day, a dispatch address that emails every order. If your legitimate correspondence volume genuinely exceeds these caps, open a support ticket describing what the mail is, roughly how much of it there is, and who receives it.

Come prepared for the conversation to start with whether the traffic should be transactional mail from an application rather than mail from a person's mailbox. In most cases it should be, and moving it is better for your deliverability than a higher cap would be.

Troubleshooting

My mail client keeps retrying and failing to send. You have most likely hit the hourly cap. Leave it for an hour, then send again. Check the outbox afterwards so you do not accidentally send the same message twice.

I have not sent 100 messages today. Check what else authenticates as that mailbox. Websites, contact forms, CRM tools, invoicing systems and monitoring scripts often use a mailbox's credentials, and their traffic counts. If you cannot account for the volume, treat it as a possible compromise: change the mailbox password from the Password tab immediately and read Account Security.

Mail is being accepted but recipients never see it. That is a deliverability problem, not a limit. Work through Why Are My Emails Going to Spam? and check Understanding Bounce Messages for what the sending report is actually telling you.

I got a bounce that mentions a rate or a policy. Read the bounce text carefully: it may be the receiving provider's limit rather than ours. Bounce codes and what they mean are covered in Understanding Bounce Messages.

I send to a list every week and it always fails partway. That is the fan-out effect. Move the list to a bulk sending service, or split the send across days if it is genuinely a one-off.

Related reading: Why Are My Emails Going to Spam?, Understanding Bounce Messages, Getting Delisted From a Blocklist, and Mailing Lists.