Learn · email signature glossary
TL;DR
An email signature logo is the company mark displayed inside a signature, usually beside or above the contact details. Technically it is an img tag pointing to an image hosted at a public HTTPS URL, since email clients need to fetch it when the message is opened. Sensible specs: 100 to 150 pixels displayed width, exported at double size for sharp rendering on high-density screens, saved as a PNG (with transparency if the mark needs it) and kept well under 100 KB. The image should carry alt text and link to the company website.
Re: In practice
The logo is what makes a signature read as a company artifact rather than a personal sign-off, and it is also the piece most likely to go wrong. Pasted or attached images can show as broken icons or turn every message into one with a paperclip attachment; hosting the file at a stable public URL avoids both. Oversized files slow message loading, and a logo dropped into the HTML at full resolution without width attributes can render enormous in Outlook, which respects the file's native size unless told otherwise. Set explicit width and height, write alt text for the many clients that block images by default, and never move or delete the hosted file, because old emails will reference that URL for years.
Fwd: Worth a look
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