Custom function to return username part of outlook emails

This is part of a bigger project I'm working on to help automate finding the first & last names of users in my Outlook global address book. I found and attempted to follow an article for retrieving Outlook address book data from Excel using a custom function to pull the username and return First Name, Last Name, etc.

But that code seems to assume that the cell value is already just the alias/username. So I have 145 cells of full email addresses I need to pull the usernames from, then attempt to use the code I found in that article to pull the Outlook information.

I'd paste screenshots, but apparently I can't because I'm still new (also it keeps flagging the example email as a link argh), so here's a small example what I need it to do, starting with only the full email.

Full Email	Username	First Name	Last Name
usrnme1[at]email-dot-com	usrnme1	User1	Name1
usrnme2[at]email-dot-com	usrnme2	User2	Name2
usrnme3[at]email-dot-com	usrnme3	User3	Name3
usrnme4[at]email-dot-com	usrnme4	User4	Name4
usrnme5[at]email-dot-com	usrnme5	User5	Name5
usrnme6[at]email-dot-com	usrnme6	User6	Name6
usrnme7[at]email-dot-com	usrnme7	User7	Name7
usrnme8[at]email-dot-com	usrnme8	User8	Name8
usrnme9at]email-dot-com	usrnme9	User9	Name9

FOR CONTEXT:
I'm having to subtract the last "[at]email-dot-com" part because the first half "usrnme" part is not the same amount of characters across all of the emails (unfortunately).

THE ACTUAL QUESTION:
I'm not sure what I'm doing wrong in being able to call the function in the B2 cell to make the cell value just that "usrme" part that it pulls from A2 and so forth. I'm trying to test it solo so I know it works before merging it with the other part I found.

I'm pretty sure I could do this, especially the last "calling it" part, by defining a range and everything...? But I feel that limits the potential of this. If it's possible I'd like to use this across multiple workbooks in the future, in the same way. Either being able to run it in individual cells (which does seem still sort of tedious), or running it as its own macro across entire Worksheets/Workbooks.

EXCEL VERSION:
I'm using Excel as part of Office 365 Apps for Enterprise, Ver 2206, on Windows 10 as the desktop app. Example book should be attached.