Outlook signature is sometimes enlarged

I have some experience with this kind of problems, as I am the developer of https://set-outlooksignatures.com.

The root is that different email clients use different HTML renderers and HTML editors, all with subtle differences.

What likely happens here is that the email client of your recipient modifies your initial HTML code before sending it. in your special case, it may convert the width and height tags and move them to style attribute, or the other way round, or remove them at all because i cannot handle width and height.

Or it could be your Outlook client, which in some versions only respects width and height when being put in the style attribute instead of directly using the according tags.

It is possible to find out the root cause of the problem, but you might end up in a situation where the root cause is out of your control because the issue happens outside of your own technical environment, or they are related to bugs on either side.

Set-OutlookSignatures and other tools used for central management and deployment of email signatures need a lot of investment to ensure that the HTML code they create is as compatible as possible with a broad range of email clients. But sometimes there are target conflicts, giving you only the choice between equally bad alternatives.