In short: Native Microsoft 365 signatures are applied by transport rules, which run after a message is sent. That produces three specific limitations: the sender never sees the signature while composing, mail sent through an SMTP relay or some mobile paths can bypass the rule entirely, and there is no central designer, preview or per-user targeting beyond what you can express in a rule. If none of those matters to you, native is genuinely enough and you should not buy anything.

Who this is for
  • You are managing signatures by hand, or by asking people to paste one in
  • Signatures render inconsistently, or users end up with two
  • Mail from an application or a relay is going out with no signature at all
  • You run several brands, regions or campaign banners and native rules have become unwieldy
What it costs to leave it

Inconsistent signatures are a small, permanent tax: every outbound email is a brand impression, and manual management means the ones that matter most, from the people who send the most, are the ones most likely to be wrong. Where a registered-details obligation applies, it stops being cosmetic.

What native Microsoft 365 signatures actually do

Exchange Online applies signatures using transport rules, sometimes called mail flow rules. The rule matches outbound mail and appends a block of HTML as the message leaves the organisation.

This works. For a business with one signature layout, no strong branding requirement and no marketing banners, it is a perfectly reasonable solution that costs nothing beyond the licence you already hold, and we would not suggest replacing it.

The limitations are all consequences of one design decision: the rule runs after send rather than while composing.

The three places native breaks

The sender cannot see it. Because the signature is applied in transit, the person writing the email sees no signature in their compose window. In practice that produces two failure modes: users add their own signature as well, so recipients get two, or users assume it is broken and start pasting one in manually. Both undermine the consistency that was the point of doing it centrally.

Replies and threads get messy. Appending at the transport layer means the block lands at the bottom of the whole thread rather than under the message just written, so long conversations accumulate signatures. Native rules can be configured to reduce this but not to solve it cleanly.

Some mail bypasses it entirely. Transport rules apply to mail flowing through Exchange Online. Mail sent through a separate SMTP relay, from an application, or by certain mobile configurations may not traverse that path, and will go out with no signature at all. If you have line-of-business systems sending mail as staff, this is the one that bites.

There is also no central design surface, no preview before rollout, and targeting is limited to what you can express in a transport rule condition. For a business with several brands, regional variations or campaign banners, that becomes administratively heavy quite quickly.

Where a signature product earns its cost

Concretely: multiple brands or trading names, regional or departmental variations, marketing banners that change on a schedule, a requirement that the sender sees the signature while composing, or mail being sent by applications that do not traverse the normal path.

Also compliance in some sectors. UK companies are required to include certain registration details on business communications, and where that obligation is taken seriously, being able to demonstrate that every outbound message carried the required block is easier with a product that enforces and logs it centrally than with a transport rule.

If your situation is one signature, one brand, and everyone works in Outlook, that list should read as none of the above, and that is the answer.

Alternatives, and switching reseller

Exclaimer is not the only product in this space. CodeTwo is the comparison that comes up most often and is a legitimate alternative, and there are others. We are an Exclaimer partner and would say so before recommending it, which is exactly why the honest version of this page has to include that it is not the only option.

One thing worth knowing if you already have Exclaimer and are unhappy: you can change reseller without changing product. That is a common and quite quiet request, usually driven by support quality or by a reseller who sold the licence and then disengaged. It does not require a migration and it does not interrupt service.

What we do with Exclaimer

  • Tell you honestly whether native Microsoft 365 signatures cover your requirement
  • Configure native transport rules properly where they are the right answer
  • Deploy and manage Exclaimer where they are not, including design and targeting
  • Fix the bypass cases, where applications or relays send mail outside the normal path
  • Take over an existing Exclaimer tenancy as reseller, without a migration

Related

Frequently asked

Can Microsoft 365 do email signatures without Exclaimer?

Yes. Exchange Online applies signatures using transport rules, which append a block of HTML to outbound mail. For a business with one signature layout, no strong branding requirement and no marketing banners, that is a perfectly reasonable solution at no extra cost, and we would not suggest replacing it. The limitations all follow from the rule running after send rather than while composing.

Why can't users see their signature when composing in Microsoft 365?

Because native signatures are applied in transit rather than in the mail client. The transport rule appends the block as the message leaves the organisation, so the compose window shows nothing. This causes two predictable problems: some users add their own signature as well, so recipients receive two, and others assume it is broken and start pasting one in manually. Both defeat the consistency that was the reason for managing signatures centrally.

Why do some emails go out with no signature at all?

Almost always because that mail is not traversing Exchange Online's transport pipeline. Transport rules only apply to mail that flows through it, so messages sent via a separate SMTP relay, from a line-of-business application sending as a member of staff, or from certain mobile configurations can bypass the rule entirely. If you have applications sending mail on people's behalf, this is usually the limitation that decides the question.

What is the alternative to Exclaimer?

CodeTwo is the comparison that comes up most often and is a legitimate alternative, and there are other products in the space. We are an Exclaimer partner, which you should weigh accordingly, and it is also why we would rather name the alternatives than pretend there are none. The more useful question than which product is usually whether you need one at all: for a single brand with a single signature layout, native transport rules do the job.

Can we move our Exclaimer subscription to a different reseller?

Yes, and it is a more common request than you might expect. Changing reseller does not change the product, does not require a migration and does not interrupt service. It is usually driven by support quality, or by a reseller who sold the licence and then disengaged. If that describes your situation, it is a straightforward change and we are happy to talk it through.

Other vendors we support

Not sure where you stand with Exclaimer?

Tell us what you are running and we will tell you plainly whether it needs action, including when the answer is that it does not.

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