Plain-English definitions of the infrastructure terms that decide whether cold email lands. Written by the team that automates all of it.
SPF is a DNS TXT record that lists which servers are allowed to send email for your domain. Receiving servers check it to confirm a message really came from an authorized sender. InboxLee publishes a single RFC 7208-compliant SPF record automatically at provisioning, so you never edit it by hand.
DKIM adds a cryptographic signature to every outgoing email that receivers verify against a public key in your DNS, proving the message was not altered in transit. InboxLee uses 2048-bit DKIM keys (not the legacy 1024-bit) and rotates them every 12 months with no customer action.
DMARC is a DNS policy that tells receiving servers what to do when SPF or DKIM fails - do nothing (p=none), quarantine, or reject - and where to send authentication reports. InboxLee defaults to p=quarantine, with a guided path to the stricter p=reject after 14 days of clean reports.
An MX record is the DNS entry that tells the internet which mail servers handle email for your domain. Sending mailboxes need the correct provider MX stack - for example the full Google Workspace stack - to send and receive reliably.
BIMI is a standard that displays your verified brand logo next to authenticated emails in supporting inboxes. It requires DMARC at an enforcement policy (quarantine or reject) first, which is why authentication comes before branding.
Inbox placement is the percentage of your sent emails that actually land in the primary inbox rather than spam or the promotions tab. It is the metric that matters for cold email, and it is different from delivery rate, which only counts whether the server accepted the message.
Delivery rate is the share of emails the receiving server accepted without bouncing. A message can be "delivered" and still land in spam, so delivery rate consistently overstates real reach - inbox placement is the truer signal.
Deliverability is the overall ability of your email to reach the inbox, shaped by authentication (SPF, DKIM, DMARC), sender reputation, content, and recipient engagement. Good infrastructure is the foundation; content and targeting do the rest.
Sender reputation is a score mailbox providers assign to your domain and IP based on sending history, spam complaints, bounces, and engagement. Low reputation pushes your mail to the spam folder regardless of content.
A blacklist (or DNSBL) is a published list of domains or IPs flagged for spam. Being listed on sources like Spamhaus, SURBL, or Barracuda can block delivery outright. InboxLee monitors 14 blacklist sources daily and alerts you on any listing.
A spam trap is an email address created solely to catch senders who use poor list hygiene. Hitting one signals that you are not verifying your lists and damages sender reputation quickly.
Bounce rate is the share of emails rejected by the receiving server. Hard bounces (invalid addresses) are the most damaging; keeping bounces low by verifying lists protects your reputation.
A seed test sends to a set of monitored inboxes across Gmail, Outlook, and Yahoo to measure real inbox placement rather than guess at it. InboxLee runs seed tests against a 24-mailbox seed list spanning Google Workspace, Microsoft 365, and Yahoo.
Email warm-up is the process of gradually increasing a new mailbox’s sending volume while generating positive engagement, so providers learn to trust it. Fresh mailboxes generally need about 14 days of warm-up before cold sending at volume.
A pre-warmed mailbox was warmed for 14+ days in a controlled environment before you receive it, so it can send cold from day one. InboxLee’s pre-warmed mailboxes are fresh accounts, never previously used by another sender.
Mailbox provisioning is the full setup of a sending mailbox: registering or connecting the domain, writing DNS authentication, and creating the account at the provider. InboxLee provisions live through the official Google Workspace and Microsoft 365 partner programs.
This is the safe number of mailboxes to run on a single domain. InboxLee caps it at 2 to 3; running 4 or more measurably drops Gmail inbox placement (by roughly 27 points in InboxLee’s testing), so additional mailboxes should be spread across more domains.
DNS is the internet’s address book. For email it holds the records - MX, SPF, DKIM, and DMARC - that authenticate your mail and route it. Cold email fails silently when these records are missing or wrong.
A sending domain is the domain your cold emails send from. Best practice is to send from secondary domains rather than your primary brand domain, so any reputation risk stays isolated from the domain your business depends on.
Cold email is unsolicited but relevant outbound email to prospects you have a legitimate reason to contact. Its success depends far more on infrastructure and deliverability than on volume - which is why authentication, warm-up, and per-domain limits matter.
InboxLee writes SPF, DKIM, DMARC, and MX for you, provisions the mailbox live, and monitors placement every day. You just send.
