Why you shouldn't use logos in Signatures

Why you shouldn't use a logo?
Trying to argue against the use of a logo in email, particularly if the request has come from a senior figure in the company can be an uphill battle. However the reasons for it are sound.
1. Makes the message larger, therefore increase the size of your Exchange store and the recipient's store. Every recipient will get a copy of the logo, on every message. If your logo is 10k, then every message you send is at least 10k, even if it has "hello" on it, and nothing else. You send ten messages to a client, that is 100k. 10 messages a day every day (which is not unusual) then that is 700k a week, which quickly builds up.
2. It can increase the likelihood of your message being flagged as spam, or as least suspicious. Everyone will have been plagued by the image spam. Therefore if your email contains an image embedded in the message, then it could get flagged. If you are looking to have the image stored remotely to avoid that and the increase in size, then that will not help either. The image could be flagged as a web bug and get the message flagged as spam.
3. You cannot control how the message will be displayed at the other end, or what the recipient is using. If you are downloading the logo from a web page, then you are presuming that the recipient has access to the internet when the message is viewed. They may not.
The recipient could be using a PDA or collecting email over a low bandwidth connection. They will not appreciate the additional bulk of your message and the logo just to have someone say "Thanks".
Once you start moving away from plain text formatting you also have the problem of display at the other end. You cannot guarantee how it will look at the end, even whether the image will remain embedded in the message or appear as an attachment. Different clients will use different ways to render the message format - ask any web developers about the problems they have with getting a web site to look the same in the various browsers in use.
Finally, to use a logo that means you have to use one of the rich formatted messages - HTML or rich text. Plain text is out of the question.
If you force the use of the logo at the server using a third party tool then any recipient of email sent using plain text may well find that the message format will be changed.
4. Do large companies send emails with logos?The final point to put across is how many large companies do you see using a logo? The answer will be none. Where a logo is used it will be something the sender themselves has done, not something that is being done centrally. It is only ever small companies that do these sorts of things - and most managers do not want to be seen as a "small company".

Logos in signatures is something that you should try and avoid where possible for the health of the server, and to try and ensure that your email is not blocked or be unwelcome by the recipients.