Getting below error email frequently from FreshService. That mailbox is operation on our exchange 2016, what exactly should we check in exchange logs for this custom mailbox as that is working fine. 

Dear Admin,

Your Freshservice custom mailbox xyz support(support@exyz.com) is unable to send outgoing emails due to 'Mailbox limit exceeded'.

What are my next steps?

• If you had sent huge volumes of emails in the last few hours, you might have reached the upper limit set by your mail service provider. Contact your mailbox provider to increase the limit or try again later.

Can Freshservice help me with this?

• Freshservice cannot help with this issue because this is a custom mailbox. We can only read and relay error messages from your mail provider.

What happens to all the tickets/emails that should be outgoing via this mailbox?

• We will queue your emails for up to 72 hours and try to send them once your mailbox reconnects. Success isn't assured though due to various factors.
• As a best practice, it's advisable to re-authenticate your mailbox within 72 hours after disconnection.