By default iPhones and iPads don't sent HTML email. And there is no built-in method for creating messages with graphics such a logos in the signature. I did have some success copying an HTML signature from an existing email and pasting it into the signature for an iPhone, but the results were inconsistent. Some devices properly sent the signature with the logo and other didn't. Even more frustrating, sometimes it started working fine and then stopped.
The solution is to implement Exclaimer Signature Manager for Exchange (www.exclaimer.com) on the Exchange server. Exclaimer manages the signature at the server level instead of at the device level. So, we don't need to worry about the type of device. It can also convert existing messages to HTML to allow the graphic logo to be embedded.
The Exclaimer software is very simple to install (almost too easy). The editing of signatures is quite intuitive and pretty easy to customize. However, I ran into problems when I was testing it.
I created a template that included the logo and applied it messages only for the Administrator account. When I sent messages, the logo appears as an attachment rather than inline in the text as it should. It looked like this:
When I was searching around, the only references I could find to logos not appearing properly suggested that it was because there were incorrect permissions for the the logo file. Network Service needs Read access to the logo. This didn't seem to apply here because the logo was being read, it just wasn't embedded properly. However, even when I gave Everyone Full permissions to the logo file, there was not fix. I also tried restarting services and disabling the antispam software running on that server. All with no fix.
If you look at the source html in the message, it does refer to the logo file with the following code, but can't seem to find it:
AdministratorFortunately, Exclaimer support was pretty quick to help me out. This server has a disclaimer configured in the hub transport rules. After disabling the disclaimer in the hub transport rules the logo was properly embedded. So, there must be an issue when both Exchange and Exclaimer try to manipulate the HTML content in the message.