Deliverability
A mail provider is only as good as its ability to actually reach the recipient. If our sending IPs pick up a bad reputation, your mail lands in spam through no fault of your own. This page explains what we do to prevent that, and what you can do on your side.
How we protect the sending reputation
No free accounts
Every Cirrux account is paid. This is the single most effective anti-abuse measure we have. Bulk spam operations depend on free, disposable signups, and a card on file plus a real billing relationship removes most of that incentive before it reaches our infrastructure.
Sending limits, lower for new accounts
Outgoing mail is rate limited at two levels: per workspace, and per individual mailbox. The per-mailbox limit is what catches a single compromised account before it can do damage to the reputation everyone else shares.
A brand new workspace starts well below the full limits and ramps up over its first month. Fresh signups are the main abuse vector, so a new account cannot immediately send at full volume. The ramp is generous enough that normal use never notices it.
Abuse response
A workspace flagged for abuse is suspended: it cannot send outbound mail, and it cannot authenticate over IMAP or SMTP. Attachments on outgoing mail are scanned for malware. Anything that threatens delivery for other customers goes to the top of the queue, ahead of feature work.
Authentication on every message
Every outgoing message is DKIM signed with a key belonging to your own domain, not a shared one. Combined with the SPF and DMARC records from domain setup, receiving servers can verify that the mail genuinely came from you.
Our own delivery, not a shared pool
Cirrux delivers directly to the recipient’s mail server from its own infrastructure, over TLS where the receiving side supports it. We do not route your mail through a bulk sending provider, so your reputation is not tied to whatever a marketing campaign somewhere else is doing that week.
Sending limits
These are the steady-state limits for an established workspace. They are set high enough that ordinary business use never reaches them, and low enough that a compromised account cannot cause lasting damage. If you have a legitimate reason to send more, email us and we will raise them for your workspace.
| Limit | Per mailbox | Per workspace |
|---|---|---|
| Messages per hour | 100 | 500 |
| Messages per day | 500 | 2,000 |
| Recipients per hour | 500 | 2,500 |
| Recipients per day | 2,000 | 10,000 |
New workspaces start lower and reach these figures over their first month.
When delivery is slow or fails
Retries and bounces
If the receiving server temporarily refuses a message, we keep retrying with increasing gaps for around two days. After roughly four hours of failure you get a one-time notice that the message has not gone through yet, so a stuck message never fails silently. If it still cannot be delivered after about 52 hours, you get a bounce.
A permanent rejection (a bad address, or a policy block on the receiving side) bounces immediately rather than being retried, and the bounce includes the reason the other server gave.
What you can do
- Finish your DNS setup. SPF, DKIM and DMARC all three, not just MX. An unauthenticated domain is the most common reason mail from a new custom domain gets filtered. See Domains & DNS.
- Warm up a new domain gradually. Receiving servers treat a domain that has never sent mail before with suspicion. A few days of normal conversation traffic settles that far better than a large first send.
- Do not send newsletters from a mailbox. Bulk marketing mail belongs with a dedicated bulk sender that handles list hygiene and unsubscribes. Sending it from a Cirrux mailbox will hit the limits above, and it is the fastest way to damage a domain reputation you depend on for real correspondence.
- Tell us when something gets filtered. If a recipient reports your mail landing in spam, forward us the details. We can check the delivery logs for the message and see exactly what the receiving server said.
Reporting a delivery problem
Delivery problems get priority over everything else we are working on. Email help@cirrux.co with the sender address, the recipient address, and roughly when you sent it. Every outgoing message is traced end to end in our logs, so we can usually tell you exactly what happened.