Corrupt email addresses in sent box

Hi DebzHow,

Can you provide more information for community members?

What version of Outlook is this?
Where is your email hosted? Exchange Online, Gmail, other?
Is it happening for all sent items or some?
If it is just some sent items, can you see a pattern such as replying to a specific domain or attempting to reply to junk mail?
Has it only just started or been this way for a while?
Anything else you think might be pertinent.

Thanks, Ash