Capacities, Limits

Mailbox Capacity

Mailbox Type Capacity Comment
Microsoft 365 Personal Mailbox 50 GB Users with A3 and A5 Plans have twice the capacity
Personal mailbox in InSIS 50 MB i.e. 1000 times smaller than Microsoft 365
Shared mailboxes in Microsoft 365 50 GB

Sending emails from the mailbox is blocked when approaching the limit; incoming emails are rejected when exceeded.

Size of Emails

Message Type Size Comment
An incoming email to school mail 15 MB Including the total size of all attachments
Emails between Office 365 35 MB It is better to upload the file on OneDrive and send only a link to the file
An outgoing email from Office 365 to the outside internet mail 18 MB It is better to upload the file on OneDrive and send only a link to the file
An outgoing email from InSIS 15 MB Such a large email will usually not be sent because the capacity of the mailbox is exceeded
Size of the message sent via 15 MB Applies to users with IMAP access to their mailbox

Office 365 – when sent using the Outlook desktop client, the maximum message size increases to 84 MB.

Number of Messages and Recipients in Message

Limit type Count Comment
Office 365 – max recipients per day 10,000 For all sent messages from one mailbox
Office 365 – maximum of recipients in one message 500 Email addresses in To, Cc and Bcc are counted – maximum of recipients per day 2,000 For all messages sent in 24 hours – maximum of emails per day 500 In 24 hours

More Information

Other limits of Microsoft 365 (A1/A3 limits apply to VŠE).

InSIS Detailed Information

Since the days when Office 365 was not used, some user groups in InSIS have a higher mailbox capacity – system integrators, managers, teachers, doctoral students. When the last role is completed, everyone’s mailbox capacity is reduced to 48 MB.
When the mailbox in InSIS is full, the emails are rejected and the set mail forwarding does not work. The so-called system messages sent from InSIS are delivered even when the mailbox is full.