01
Which calendar is actually being shared?
Confirm the exact mailbox address and calendar. Do not assume the user's other company address is in the same tenant.
Everyday IT · Calendars
Calendar sharing starts with the mailbox and tenant.
Two addresses that look related can live in different Microsoft 365 tenants and follow different sharing policies.Identify the mailbox, identify the tenant, then check the sharing policy.
What to check first
02
Which tenant owns that mailbox?
Find the mailbox in the correct Microsoft 365 tenant before changing policies or permissions.
03
Which sharing policy applies?
Check the mailbox's assigned sharing policy and whether it allows calendar sharing to the recipient's domain.
04
Test with the exact external domain
After the policy is confirmed, test the same sharing workflow with the intended domain and verify with the user.
Do not troubleshoot the wrong tenant.
If the mailbox belongs somewhere else, settings in the first tenant will never fix that calendar.