Email signature generator › Embedded or hosted

Embedded or hosted: choosing how the logo travels

An image in a signature either travels inside the message or is fetched from a server. The two choices fail in opposite ways, and which failure you prefer is genuinely a decision rather than a best practice.

The two mechanisms

Hosted. The signature carries src="https://example.com/logo.png". Nothing travels with the message. The recipient's client downloads the file when the message is opened — if the reader allows remote content.

Embedded. The image is carried inside the message, either as a separate part referenced with src="cid:..." or, less commonly, as a data URI inline in the markup. Nothing is fetched. It always displays.

What each one costs

Hosted costs nothing in weight and depends on two things outside your control: the reader allowing images, and the URL still resolving. A share of recipients — everyone on Proton, most Outlook users receiving external mail, anyone who turned it off — sees the alt text instead.

Embedded always displays and adds roughly a third to the image's size in encoding overhead. A 30 KB logo becomes about 40 KB, on every message. It also produces a paperclip in the clients that list inline parts as attachments.

The arithmetic that usually decides it

Gmail truncates a message at around 102 KB and hides the rest behind a link. An embedded 40 KB logo on a thread of three messages is 120 KB — already past it. The part that gets hidden is the older history, which is exactly what people scroll to for context.

So: if you have long threads with external correspondents, host it. If your correspondence is short exchanges, the weight does not matter and the reliable display is worth more.

Data URIs specifically

A data URI puts the encoded image directly in the src attribute. It is convenient and it is the worst of the three options for email: Gmail strips data URIs in images entirely, Outlook handles them inconsistently, and the encoded string bloats the markup itself rather than sitting in a separate part. Use a proper embedded part if you embed at all.

The permanence question

A hosted logo breaks the day the URL stops resolving, and it breaks backwards: every message in every archive loses it at the same moment. An image carried inside the message has no such dependency — it is as durable as the message itself.

For most people this is a curiosity. For anyone whose sent mail is evidence — legal practice, regulated advice, contract negotiation — it is the argument that settles the question in favour of embedding.

Alt text matters either way

With hosted images, the alt text is what a blocked reader sees, which makes it the actual content for a meaningful share of your audience. With embedded images, it still shows while the message loads and in clients that fail to render the part. alt="Acme", never alt="logo" and never empty.

A rule of thumb

Host it, keep it under 20 KB, put nothing in it that the text does not also say, and give it real alt text. That is right for most people. Embed it only when you have a specific reason — an audience that blocks images, or a requirement that the record stay complete — and accept the paperclip and the weight as the price of it.

The numbers, laid out

A wordmark displayed at 160 pixels wide, exported at 320 for sharpness and optimised, lands around 8 KB. Hosted, it adds nothing to the message. Embedded, the encoding brings it to roughly 11 KB, and that is per message — so a ten-message thread carries 110 KB of the same logo and has already passed Gmail's 102 KB clipping point.

If the logo is a full-colour graphic rather than a wordmark and weighs 40 KB, embedding puts the thread over the limit by the second reply.

A middle path

Embed on new messages, where the first impression happens and the thread is short; use a text-only signature on replies. Most clients support a different signature for replies, and it resolves the trade rather than choosing a side of it — the logo always displays where it matters, and the thread never accumulates copies.

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