Add "_" before all SMTP addresses in Exchange - email

Question

I'm looking script that help me to add "_" before all SMTP addresses in Exchange.
Let's say we have a user John Doe. John has 3 different SMTP addresses:
john.doe#contoso.com
jdoe#domain.com,
john#contoso.com
I'd like to change disable all features in Exchange (like OWA, ActiveSync and so on), hide his account in GAL and set all his addresses to:
_john.doe#contoso.com
_jdoe#domain.com,
_john#contoso.com
I can do it for primary SMTP but I can't for rest of them :(
For Now I have try such solution:
Set-Mailbox $sam -HiddenFromAddressListsEnabled $true -DomainController $dmc
Set-CasMailbox $sam -OWAEnabled $false -ActiveSyncEnabled $false -MAPIEnabled $false -PopEnabled $false -ImapEnabled $false -DomainController $dmc
mbx = Get-Mailbox $sam -DomainController $dmc | select -expand EmailAddresses | %{$_.SmtpAddress}
foreach ($M in $mbx)
{
[string]$email += "'smtp:_"+$M+"',"
}
but it doesn't works for me. I'm quite fresh in PS so could you please help me.

Answer 1

Multiple issues:
The main problem is that you're generating a list of the new addresses, but you're not modifying the mailbox objects. Just running a foreach loop against results queried from a mailbox isn't going to modify that object. You need to use Set-Mailbox to actually set the new addresses:
Set-Mailbox -EmailAddresses <new_addresses>
The way you're creating the string, it will have a trailing comma. If you want to create a comma-separated string from strings generated by a loop, do it this way:
$email = $(foreach ($m in $mbx) {
"'smtp:_" + $m + "'"
}) -join ','
The loop returns an array of the strings generated by each iteration, and the -join ',' joins them into a comma-separated string.
That said, you actually don't want to join them into a comma-separated string, because the -EmailAddresses parameter of Set-Mailbox takes an array argument. So, you just want to use the return value of the loop as the argument.
Adding the smtp: prefix is unnecessary because that's the default.
On the other hand, if you're only modifying SMTP addresses, you do want to use Where-Object to filter the contents of the EmailAddresses property for SMTP addresses:
?{$_.Prefix.ToString() -eq 'smtp'}
Putting it all together:
foreach ($mbx in (Get-Mailbox <whatever>)) {
$modified_addresses = $mbx.EmailAddresses `
| ?{$_.Prefix.ToString() -eq 'smtp'} `
| select -ExpandProperty EmailAddresses `
| %{"_$_"}
Set-Mailbox $mbx -EmailAddresses $modified_addresses
}