Things that increase scan time:
1. OCR
2. Resolution
3. Quality/File Size settings
4. Scan via host name instead of IP
Then of course there is the protocol in use.
Scanning speed fastest to slowest in general will be:
1. USB
2.FTP
3.SMBP
4.Email
If email, there is often an issue after multiple scans where the scan goes through the machine and shows complete, yet sits in a netherrealm and does not appear in your email account for minutes, to hours.
If that last one is the issue, get the email provider to whitelist the device, but in the mean time, change the filename, subject line and message body of the email, reboot and resend.
The reason is that the SMTP server assumes a spam account, we know without a doubt that Gmail and Office365 and Comcast do this, and for good reason.
In the eyes of the SMTP server it sees a user (Printer and its email address) that sends literaaly the exact same email constantly, nothing ever changes. While you may be putting entirely different jobs through the device, all the mail server sees is all the same things.
1. From account
2. Subject line
3. Message body
4. Footer
5. Signature
6 Attachment (doc.pdf every single time)
The only things that change are the address you send to, and the file size.
So in the shorter term you can just change those things, but that will be short term, the other is to have the device IP and from address entered into a white-list at the SMTP server so that it is not caught up in the filters.