Four things decide where a message lands: domain authentication, sending pace, list quality and unsubscribes. A step-by-step breakdown, without the myths.
A spam filter does not read your message the way an editor would. It looks at the
sender: is the domain authenticated, how fast the mail goes out, whether people complain,
whether the addresses are real. The text matters last — and the word "free" in a subject
line does not sink a message.
Below is what actually decides, in order of weight.
Why messages land in spam
There are five reasons, and they almost always work together:
The domain is not authenticated. The recipient's mail system cannot
verify that you sent the message and not somebody using your name.
Too fast. A hundred messages a minute from a mailbox that sent three
yesterday is the most visible sign of bulk mail.
A bad list. Dead addresses, old databases, spam traps. Every bounce
damages the sender's reputation.
Complaints. The Spam button is the one signal that outweighs
everything else. Google treats anything under 0.3% as normal.
No way to unsubscribe. When there is no unsubscribe link, people
press Spam — it is the only way left to stop the mail.
SPF, DKIM and DMARC in plain words
Three records in your domain settings that together answer the question "is this
message really from them?":
Record
What it tells the receiving mail system
SPF
Which servers are allowed to send mail for this domain at all.
DKIM
A cryptographic signature: the message was not altered in transit.
DMARC
What to do when a check fails, and where to send the reports.
If you send from a regular @gmail.com address there is nothing to
set up: gmail.com is signed by Google itself, and messages from your mailbox
already pass all three checks. That is one of the reasons to send from your own mailbox
rather than from a bulk service's shared domain.
If you are on Google Workspace with your own domain, SPF, DKIM and
DMARC have to be switched on by hand in the admin console, once. Google
requires them from every bulk
sender, and from large ones it also requires one-click unsubscribe and a complaint
rate under 0.3%.
Pace: why a thousand messages a minute is a bad idea
A steady stream of identical messages in the same second is a machine's handwriting,
and it reads exactly like one. A normal pace looks different: a pause between messages, a
sensible daily volume, gradual growth.
A pause between messages. MailSharks uses a randomised delay of
5 to 10 seconds rather than a fixed one: an exact interval looks
machine-made on its own.
A daily cap. 100 messages per campaign by default, with
a ceiling of 2000 per mailbox. Details on the
Gmail limits page.
A warm-up. A new mailbox should not start with five hundred messages.
Make the first campaign a few dozen addresses and grow from there.
The list: why purchased databases kill a sender
A bought list is the fastest way to ruin a mailbox's reputation, for three reasons:
Such lists are full of dead addresses, and every bounce is recorded against you.
They contain spam traps — addresses nobody ever created for
correspondence; mail arriving there means the list was not collected honestly.
People who were not expecting you complain more often. A handful of complaints per
thousand is enough to send the next messages to spam for everyone.
The only list that works is one where people left their address themselves: customers,
subscribers, attendees, people you have corresponded with. Mailing purchased lists is
forbidden by the MailSharks terms.
Unsubscribes are not a formality
An unsubscribe link removes complaints: somebody who can leave in one click has no
reason to press Spam. Three things have to work:
The List-Unsubscribe header. The one that makes Gmail show an
Unsubscribe button next to the sender's name. MailSharks adds it for you.
A visible link at the end of the message. Not light grey on white,
and not inside an image.
Immediate effect. Anyone who opts out joins the sheet's suppression
list, and the next campaign skips them — even if the address is still in the sheet.
The message itself
The text decides less than people think, but silly mistakes are still worth avoiding:
A subject line without ALL CAPS, without "!!!", and without promises the message does
not keep.
A greeting by name instead of "Dear customer" — the {{name}}
placeholder takes the name from your sheet.
One link to one action instead of ten. Avoid link shorteners (bit.ly and friends):
their reputation is shared with thousands of other campaigns.
A message that is one big image is a bad idea: the filter has nothing to read, and
half the recipients will not load images anyway.
A first message to a stranger does not need an attachment.
If your mail is already going to spam
Slow down. Cut the daily cap several times over and start no new campaigns for
a week.
Clean the list. Remove every address that bounced and everyone who has not
opened a single message in the last six months.
Ask real recipients. Have one or two people you write to personally pull the
message out of spam and reply to it — a reply repairs reputation faster than anything
else.
Look at the numbers. For your own domain, use
Google Postmaster Tools:
it shows the complaint rate and the state of your reputation.
