How do I add a txt file to read from in the following script

Question

First thanks for the help, PS newbie. 
I need to add a txt file that has the Exchange aliases listed to the below file. So if the .txt file is sitting in c:\temp\readme.txt how do I incorporate into the following script. Given, I only want the outcome to read from only the txt file. 
$mailboxes = Get-Mailbox -RecipientTypeDetails UserMailbox
ForEach ($mailbox in $mailboxes) {
  $FilePath = "\\server\folder\" + $mailbox.PrimarySmtpAddress.Local + "@" + $mailbox.PrimarySmtpAddress.Domain + ".pst"
  New-MailboxExportRequest -mailbox $mailbox -FilePath $FilePath
Thank you for your time. 
Chris

Answer 1

Thank you - 
You're welcome.
I need to make sure that when the user from the list is exported to .pst it is named with their primary smtp address? Will the above code do so?
No, it won't. This adjustment will take that into account:
$aliasList = Get-Content .\aliasList.txt
foreach ($alias in $aliasList) {
$mbx = Get-Mailbox $alias
$filePath = "\\server\folder\$($mbx.PrimarySmtpAddress).pst"
New-MailboxExportRequest -Mailbox $alias -FilePath $filePath -WhatIf
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