Email Logo is insert into the header and footer of the 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 visitor. Therefore, right after installing Magento 2 successfully, the first of all is replacing the Magento 2 Defaul Logo by your own logo.
The logo accepts many types of the image field including 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 ensure that your logo is displayed clearly on high-resolution devices, should upload that image whose dimension is three times as large as the required size in the header. If you don’t know the size of the logo, or any image that is 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
Content > Design > Configuration.
Uploadto choose one of the image file you want to aplly for your logo.
Logo Image Alt.
Logo Heightin pixels. Just enter the number that don’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 have 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.