Email Logo is inserted into the header and footer of a transactional email message. Similarly to the Store Logo, the Email Logo is also one of the best ways for the audience to identify your brand easily and at same time, your store becomes more reliable to the visitors. Therefore, right after installing Magento 2 successfully, the very first thing to do is replacing the Magento 2 Default Logo by your own one.
The logo accepts many image types such as JPG/JPEG, GIF, PNG, or SVG, and it is flexible to customize the size of the logo from Magento 2 Admin. However, I have a tip for you to make it done more easily. To ensure that your logo is displayed clearly on high-resolution devices, you should upload an image that its dimension is three times as large as the required size in the header. If you don’t know the size of the logo, or of any image used in your theme, just right-click on the image on your site, and inspect the element to get its size.
Two following steps will help you know what you can do to change Email Logo in Magento 2
Stores > Settings > Configuration.
On the Admin sidebar,
Content > Design > Configuration > Select your current theme > .
Uploadto choose one of the image files you want to aplly for your logo.
Logo Image Alt.
Logo Heightin pixels. Just enter the number that doesn’t include “px” symbol. The appearance of the email logo in the header depends on the offered value size instead of the real size of the logo.
If you want to modify Header and Footer templates or if you run multiple stores, you can assign a specific template to each, that will appear on the transactional email message.
Footer Templatefrom the available list as needed.
Save Configto finish and the design of the email is active.
Ref: Magento 2 User Guide
It comes to the end of tutorial: How to change Email Logo in Magento 2.