Outlook's default attachment limits
According to Microsoft's official support article on the “attachment size exceeds the allowable limit” error, checked in September 2026, classic Outlook 2013 and later has a default limit of 20 MB for internet email accounts, such as POP3 and IMAP. Exchange mailboxes default to 10 MB unless an administrator changes it.
Work and school accounts often have their own limits. If you use an Exchange mailbox, change the target in the compressor to about 9,700 KB, or ask your IT team what applies to you.
It's the total that counts
The limit covers all attachments in one message together. Two 12 MB PDFs are 24 MB and won't go through, even though each file alone is under 20 MB. Compress each file to a lower target so the total fits, or send them in separate emails. Remember that the recipient's provider may also accept less than you can send.
How ConvertirDocs shrinks your PDF
Only the photos inside the PDF are recompressed: scans, pictures and images in reports. Text and vector graphics are left alone, so typed text stays sharp and selectable. The tool shows the size before and after, and if it can't reach the target, it explains why.
It's 100% free, with no account. Everything runs in your browser, so your file never leaves your device.
Common mistakes and what to do if it still won't send
Compressing until the document is unreadable doesn't help anyone; zoom in on small print, numbers and signatures before sending. If quality suffers, delete pages nobody asked for with “Remove pages”, or split the PDF with “Split PDF” and send it in two emails.
If Outlook still refuses, add up the sizes of all attachments in the message and check whether your account is an Exchange mailbox with a lower limit.