try to add save_attachments parameter
When set to true the content of attachments will be included in the attachments.data field.
input {
imap {
host => "outlook.office365.com"
port => 123
user => "user@abc.com"
password => "******"
check_interval => 3600
fetch_count => 100
folder => "Inbox"
content_type => "application/gzip"
save_attachments => true
}
}