what can I do to fill a variable with multiple value using foreach loop

I need to fill the variable $navmailbox with all mailboxes that belongs to nav company but I can’t do that with the below script as $navmailbox only take the last value. The $navmailbo does not add a new  value to the old value in other words , if $navusers=peter,lydia $navmailbox will only contains the last mailbox of lydia not peter and lydia 

what can I do to fill a variable with multiple value using foreach loop

$navusers=get-user | ? {$_.Company -eq "navt"} foreach($mailbox in $navusers) {$navmailbox=get-mailbox -id $mailbox.name}

if $navusers=peter,lydia $navmailbox will only contains the last mailbox of lydia not peter and lydia 

why I need that because I want a script that ouput the quota of nav company mailboxes with their database limit

 I made a simple script to get the quota of some users in a specific company

$navusers=get-user | ? {$_.Company -eq "navt"} foreach($mailbox in $navusers) {get-mailbox -id $mailbox.name | select name,ProhibitSendQuota,ProhibitSendReceiveQuota,database}

this work fine but I want to know the database limits ,so I need the get-mailboxdatabase command so I edited the script to be like that but the field "DBwarninquota"is displayed without values as shown below

$navusers=get-user | ? {$_.Company -eq "nav"} foreach($mailbox in $navusers) {get-mailbox -id $mailbox.name | select name,ProhibitSendQuota,

ProhibitSendReceiveQuota,@{n="DBwarninquota";e={(get-maiboxdatabase -id $_.database).ProhibitSendQuota}}}

I think this is because the variable $mailbox.name doesn't contain the properties of mailbox it contains the properties of users

I think that I should have a variable that contains the mailboxes of navusers, I can't fill a variable with all the mailboxees using this command