MailerLite deliverability: the checks that matter before blaming the platform

MailerLite runs shared sending infrastructure with optional custom-domain authentication, and the pattern behind most reported deliverability drops is consistent: a custom domain missing full authentication, a list carrying unengaged or invalid addresses, or content that trips engagement-based filtering at a specific provider. The platform's baseline sending reputation is rarely the actual cause.

Authentication gaps on a custom domain

A custom sending domain connected to MailerLite needs an SPF record authorizing MailerLite's sending servers and a DKIM record with the selector value MailerLite's own domain-authentication page provides for that account - copy it from there directly, since the value is specific to your setup and guessing at it produces a record that looks plausible but never validates. A domain missing either record can pass MailerLite's own setup checklist while still failing authentication at the receiving server.

List hygiene signs worth checking first

Content and engagement-based filtering

Modern spam filtering weighs recipient engagement heavily - a campaign sent to a segment that rarely opens mail signals low relevance to the receiving provider, independent of the content itself. This is why the same campaign can land in the inbox for an engaged segment and in spam for a stale one, even sent from the identical domain in the same send. Segmenting by recent engagement before a send, rather than mailing the full list every time, is one of the more effective and underused levers here.

What MailerLite's own analytics do and do not show

MailerLite reports opens, clicks, and bounces per campaign, which flags a problem but does not distinguish inbox placement from Promotions-tab placement from spam-folder placement - all three can produce a similarly low open rate, and only placement testing against real seed inboxes across providers tells them apart.

What not to do

Do not re-send to a full list, including long-inactive subscribers, to "boost" a flagging campaign's numbers - mailing a stale segment is more likely to generate spam complaints that hurt the sending domain's reputation than to recover engagement. Do not assume a custom domain is authenticated just because MailerLite's setup wizard marked it as connected; verify the actual DNS records resolve correctly.

Why the same account can see mixed results across providers

It is common for a MailerLite account to see healthy placement at one major provider and a problem at another simultaneously - each receiving provider runs its own independent filtering logic, with its own thresholds for engagement and its own view of the sending domain's history there specifically. A domain-wide authentication fix or list cleanup usually improves placement everywhere, but recovery timing differs by provider, so checking placement one provider at a time, rather than looking for one aggregate number, gives a clearer picture of where a problem actually persists.

When a platform migration is the real cause

Accounts that recently moved to MailerLite from another ESP sometimes carry over list-hygiene problems that existed before the move but were masked by an older platform's longer sending history. A fresh platform migration is worth treating as a reason to run a full list audit and re-confirm authentication from scratch, rather than assuming settings that worked on a previous platform transferred over correctly - selector values and SPF includes are provider-specific and do not carry over automatically.

One more thing worth ruling out

If placement looks fine at every major provider individually but overall engagement still seems low, check whether a large share of the list is on a corporate domain with aggressive link-scanning or attachment-stripping security gateways - these can suppress open and click tracking without affecting inbox placement at all, producing a metric that looks like a deliverability problem but isn't one.

Why this distinction is worth confirming before escalating further

Corporate link-scanning can make a campaign look like it is underperforming by every tracked metric MailerLite reports, while the mail itself is landing in the inbox exactly as intended - the scanner, not the human recipient, is triggering (or suppressing) the tracked event. Confirming this with a quick cross-check against a personal, non-corporate test address prevents chasing a deliverability fix for a problem that is actually just a measurement blind spot.

Where MailPilot fits

MailPilot checks SPF/DKIM/DMARC against live DNS for custom domains connected over SMTP/IMAP, warms mailboxes gradually, runs seed-inbox placement tests across providers, and tracks per-mailbox reputation daily - giving MailerLite senders the placement visibility that open-rate reporting alone cannot provide.