Relevant Products: Exclaimer Cloud - Signatures for Office 365 | Exclaimer Cloud - Signatures for G-Suite
When using a signature template that has large elements, using a fixed size or large banners. Emails received on iOS devices (more specifically iPhones) you will notice the email re-sizes to "Fit to Screen"
This happens because the iOS devices are designed to fit anything onto the screen. You may see when opening an email that the email will suddenly jump from being normal reading size to a much smaller size. This is because the email being sent has some element within it that is larger than the devices screen size and will reduce the email to fit on the screen.
Unfortunately, because this is a specific device setting, it is something that we cannot fully control. We have a set of advisory guidelines that we can advise the customer to take in order to reduce this is as much as possible. But we cannot fully stop it from happening.