Auto complete on iMac- edit list of replacements
You can add a shortcut that replaces a misspelling, so when you type your email address it will autocorrect to the same address (if that makes sense).

Click System Preferences > Keyboard > Text, and click the (+) button to add a new shortcut. Type your email address in the "replace" column and the same email address in the "with" column.

This will ensure you type your correct email address but then it will stay, and not autocorrect.