Why is there a strange prefix in my domain settings on Shopify?

[Frank_Query]

In shopify/ domain settings the 2nd line (of usually 3 lines) with the redirects and the .myshopify.com my shop name shows a weird prefix to the .myshopify.com record.

I do have another webshop where all 3 lines in the domain section are correctly spelled as "myshop_1".

That "funny name record" earlier was also given as sender address for emails at times, very annoying as we'd want to display our proper email address of course.

[StephensWorld]

When you go into the domain settings (Admin > Settings > Domains), under the myshopify.com URL, there should be a link for "change to a new myshopify.com domain" which you can click to change to a different handle. 

However, if you add a custom domain name (ex. yourstore.com), the custom domain will replace the myshopify.com URL, so customers will only see your custom domain name ... so it doesn't really matter what the myshopify.com URL is. 

With regards to the sender email address -- you can edit this from your notifications settings (admin > settings > notifications). 

It's best to use a professional email address for this, which you can usually purchase via your domain provider (if you didn't buy the domain via Shopify). I recommend using GoDaddy for purchasing professional email addresses (https://www.godaddy.com/en-ca/email/professional-business-email). Once you've purchased a professional email address, and added it to the 'notifications' settings on Shopify, you'll need to add some DNS records so that Shopify can send emails from this address. You'll see some instructions on the 'notifications' settings page for what those records need to be. 

You'll also want to set up a DMARC text record for your domain. I've posted instructions for setting up a DMARC record on this thread: https://community.shopify.com/c/shopify-discussions/dmarc-is-complicated-or-is-it-just-me/m-p/236929... 

[Frank_Query]

Dear @StephensWorld  thanks for your elaborate response.

1. When using the link we get the error "Third level domain is invalid".

2. We added a GoDaddy domain and emails and this works now, thank you, can be accessed properly via the correct name/ url.

3. I still get such message recently: "The following changes were recently made for your store https://7f9eed5.myshopify.com/admin"

So, this is not so nice in that I do not know to which store it links precisely AND I feel for some reason this link is being used still at various places. Even our app support team refers to this for some reasons.

4. The dmarc record I tried following the links and all... still not sure what if this is not related my questions above, please let us ignore it for the moment. As I said, all works fine except occasional link/ message related to this funny url.