Return Secondary SMTP Addresses that prefix with SMTP

Question

I am running the following command which returns a few properties along with all the secondary addresses. The issue I need to resolve is to filter all secondary addresses which do not begin with "smtp". I also do not want to return
the case sensitive version of smtp: "SMTP"
Output Below:
Get-Mailbox UnityVM -DomainController DC05-ResultSize Unlimited | Where {(!($_.RecipientTypeDetails -Match "RoomMailbox|SharedMailbox"))} | Select-Object DisplayName,alias,Identity,ServerName,RecipientTypeDetails,PrimarySmtpAddress, @{Name=“SecondaryAddresses”;Expression={$_.EmailAddresses
-join "`n"}}

Answer 1

This thread appears to be abandoned.  Here is the crux post by the OP.  I reformatted for clarity
Get-Mailbox crusso -DomainController DC01 -ResultSize Unlimited |
Where {(!($_.RecipientTypeDetails -Match "RoomMailbox|SharedMailbox"))} |
Select-Object DisplayName,
alias,
Identity,
ServerName,
RecipientTypeDetails,
PrimarySmtpAddress,
Name="SecondaryAddresses";
Expression={
$mbx.EmailAddresses|Where {$_.ProxyAddressString -cmatch '^smtp:'}
The OP asked a specific and narrow question but has added a convoluted and unstated complexity at the end. I suspect the thread was abandoned when the OP realized the problem.  In reality most of the solutions answer the original question.  The
legerdemain actually alters the question.
Look closely at the whole code snippet and note that the OP has no understanding of PS and has just blindly added the examples into code that was likely copied from yet another forum.
Using PowerShell without the brain disengaged is foolish.  It is like flying an airplane blindfolded.  It can be done but often leads to a crash.
Notice how I was able to adeptly slip in "the word of the day" and yesterday's "word of the day" and now tomorrow's "word of the day".  Pretty good, huh?
Ciao..  a presto!
¯\_(ツ)_/¯