Exchange: How to reliably determine that a user is logged into mailbox?

Sometimes (for example while migration users are from another email system) there is a need for reliable determination that a user is logged into the mailbox (using Outlook or OWA).

The simplest answer is mailbox's lastlogontime (Get-MailboxStatistics). But it turnes out to be not quite true.
Attention! The attribute "LastLogonTime" of user's mailbox filled and updated when another user opens user's calendar.

Finally, I found 4 criterias which help to reliably determine that a user is logged into the mailbox.

1. "lastlogontime" (Get-MailboxStatistics) - necessary but not sufficient attribute.
2. "Languages" (Get-Mailbox) - this attribute filled when user entered into OWA and sometimes filled when entered into Outlook.
3. "WorkingHoursTimeZone" (Get-MailboxCalendarConfiguration) - this attribute filled when user entered into OWA and sometimes filled when entered into Outlook. Deffault value - "Pacific Standard Time", so you can use it only if users are in a different time zone.
4. "Quick Step Settings" (Get-MailboxFolderStatistics) - this is not an attribute, it is a checking for the presence of a folder "Quick Step Settings" in the mailbox, because it appears only when you open/configure Outlook.

Examples

User 1 - active user. User2 - new user

[PS] C:\Windows\system32>Get-Mailbox user2 | Get-MailboxStatistics | ft Displayname,lastlogontime,lastlogofftime
DisplayName                             LastLogonTime                           LastLogoffTime
-----------                             -------------                           --------------
User2

[PS] C:\Windows\system32>Get-Mailbox user1 | Get-MailboxStatistics | ft Displayname,lastlogontime,lastlogofftime
DisplayName                             LastLogonTime                           LastLogoffTime
-----------                             -------------                           --------------
User1                                   12/26/2017 11:45:14 PM                  12/26/2017 11:59:53 PM

[PS] C:\Windows\system32>Get-Mailbox user2 | ft name,Languages
Name                                                        Languages
----                                                        ---------
User2                                                       {}

[PS] C:\Windows\system32>Get-Mailbox user1 | ft name,Languages
Name                                                        Languages
----                                                        ---------
User1                                                       {en-US}

[PS] C:\Windows\system32>Get-MailboxCalendarConfiguration user2 | fl identity,WorkingHoursTimeZone
Identity             : test.local/Users/User2
WorkingHoursTimeZone : Pacific Standard Time

[PS] C:\Windows\system32>Get-MailboxCalendarConfiguration user1 | fl identity,WorkingHoursTimeZone
Identity             : test.local/Users/User1
WorkingHoursTimeZone : Eastern Standard Time

For convenience, I presented the test results in the table:

Scenarios	lastlogontime	Languages	WorkingHoursTimeZone	"Quick Step Settings" Folder
New mailbox	-	-	Pacific Standard Time	-
Active user	Sunday, July 29, 2018 3:31:58 PM	en-US	Eastern Standard Time	Present
User logged into mailbox by OWA	Sunday, July 29, 2018 10:46:31 PM	ru-RU	Russian Standard Time	-
User logged into mailbox by Outlook	Sunday, July 29, 2018 10:53:15 PM	-	tzone://Microsoft/Custom	Present
Another user opened user's calendar	Sunday, July 29, 2018 5:34:37 PM	-	Pacific Standard Time	-
Another user (with Full Access) opened user's mailbox	Sunday, July 29, 2018 6:34:03 PM	-	Pacific Standard Time	-

Result

To sum up, to accurately determine whether the user entered the mailbox or not, you can use the following set of commands:

$User = "user1"
$User_Enter_LogOn = (Get-Mailbox $User | Get-MailboxStatistics).lastlogontime
$User_Enter_Languages = (Get-Mailbox $User).Languages.Count
$User_Enter_TimeZone1 = (Get-MailboxCalendarConfiguration $User).WorkingHoursTimeZone
$User_Enter_TimeZone2 = (Get-MailboxCalendarConfiguration $User).WorkingHoursTimeZone.ExTimeZone.Id
$User_Enter_QuickStep = (Get-MailboxFolderStatistics $User | where {$_.name -eq "Quick Step Settings"}).name
if (($User_Enter_LogOn -ne $null) -and (($User_Enter_Languages -ge 1) -or ($User_Enter_TimeZone1 -eq "tzone://Microsoft/Custom") -or($User_Enter_TimeZone2 -ne "Pacific Standard Time") -or ($User_Enter_QuickStep -eq "Quick Step Settings")))
{
# User is logged in.
}
else
{
# User did not logged in.
}