Deliverability has its own language — authentication records, bounce classes, suppression lists, warm-up curves. Here are the terms that actually decide whether your mail arrives, defined plainly and without hand-waving.
The records that prove a message really came from you. mailstein publishes and manages all of them for every domain you add.
A DNS TXT record listing which servers are allowed to send mail for your domain. When a receiving server sees a message from your domain, it checks whether the sending IP appears in your SPF record. If it does not, the message looks forged.
A cryptographic signature added to every outgoing message, verifiable against a public key published in your DNS. It lets receivers confirm the message body and key headers were not altered in transit and genuinely originated from your domain.
A policy record that ties SPF and DKIM together and tells receivers what to do when a message fails both — deliver, quarantine, or reject. It also requests aggregate reports so you can see who is sending under your name.
DMARC passes only when the domain in the DKIM signature (or the SPF check) matches the visible From address. A message can carry a valid DKIM signature and still fail DMARC if that signature belongs to a different domain. Alignment closes that gap.
The hidden address that receives bounce notifications, separate from the visible From address. It is the domain checked by SPF and the destination for delivery failures, which is why it must be a domain you control and monitor.
Mail Exchange records in DNS that tell the world which servers accept inbound mail for a domain. Sending is governed by SPF, DKIM, and DMARC; MX records govern receiving. You need correct MX entries to catch replies and bounce reports.
What happens after you press send — and how a healthy sender responds to it. mailstein tracks every one of these events per message.
A permanent delivery failure — the address does not exist, or the domain rejects it outright. Hard-bounced addresses should never be retried; continuing to mail them signals poor list hygiene and drags down your reputation.
A temporary failure — a full mailbox, a server briefly unavailable, or greylisting. Soft bounces can be retried on a sensible schedule, but repeated soft bounces to the same address eventually behave like a hard bounce.
Registered when a recipient clicks “report spam.” Mailbox providers share these through feedback loops, and even a low complaint rate — well under one percent — can throttle your delivery. The only cure is relevance and a clear unsubscribe path.
A running record of addresses you must not send to — hard bounces, complainers, and unsubscribes. A good platform enforces it automatically on every send so a bad address can never slip back into a campaign by accident.
The slower-moving forces that decide your ceiling — and the terms that come up when you own your own sending, the way mailstein does.
A sending IP used only by you, rather than shared with thousands of other senders. Your reputation is entirely your own — no neighbor's bad behavior can taint it, and no one benefits from or damages your standing but you.
The practice of gradually increasing send volume on a fresh IP so mailbox providers build trust instead of flagging a sudden spike as an attack. Skipping it is the most common reason new senders land in spam. mailstein manages the ramp for you.
The score mailbox providers assign to your domain and IP based on complaints, bounces, spam-trap hits, and engagement. It is earned slowly and lost quickly, and it is the single strongest predictor of whether you reach the inbox.
One-to-one mail triggered by a user action — password resets, receipts, verification codes. It must arrive within seconds and is expected by the recipient, so it carries the highest deliverability stakes of anything you send.
One-to-many mail sent to an audience — announcements, newsletters, product updates. It leans harder on reputation and engagement because recipients did not individually trigger it.
An address that exists only to catch senders with poor hygiene — either a never-used address seeded by providers, or an old one recycled into a trap. Hitting one is a strong signal you are mailing a list you did not clean, and it can cost you dearly.
SPF, DKIM, and DMARC configured automatically. Dedicated IPs with managed warm-up. Bounce and complaint suppression on every send. Start on the free plan — 50 emails a month, one domain, no card.
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