Hi there 

Thanks for your post! Just to make sure I understand the issue correctly your user has two corporate email addresses and they’re not receiving invites to collaborate on documents because the team is sharing those documents with one of those emails while your user’s account is associated with the other? If so your user can change the email address connected to their account through their User Settings page so that it matches to the email used by the team to share documents with them. For more information please have them view our Account Settings Help Center article. 

As for your suggestion while it’s currently not possible to have multiple email addresses associated with a user account we're always looking for ways to improve Lucidchart and your feedback is the best way for us to do that. Would you mind adding your idea to our feature request form? Ideas submitted to this form are passed on to the product development team for their consideration. Thanks for your feedback!

If your user runs into any trouble while trying to make the email change please have them submit a support ticket by filling out this form so we can help them out. Thanks!