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Email Not Sent – Attachment Size Limit Exceeded

If you get the error "This email wasn't sent" in HubSpot, the most common cause is that the total size of your attachments or inline images exceeded the allowed limit.  

Symptoms

  • A red banner on the email in the contact's timeline: "There was an issue sending your email. This email wasn't sent."
  • No bounce is recorded for the recipient's email address.
  • The email contains multiple large photos pasted inline or attached as files.

How to Check the File Size (Windows)

Before sending, check the total size of your files:

  1. Locate your files in File Explorer.
  2. Right-click on a file and select Properties to see the file size.
  3. Add up the sizes of all files. The total must be under 20 MB (20,000 KB). If using Outlook, keep it well under 4 MB.

Solutions

Option 1 – Share files as links from HubSpot 

This is the best option when files are too large to attach or compress.

  1. Upload your files to the HubSpot File Manager (Files tool).
  2. Open the file in the File Manager. You will see options at the top: Share internal link, Share 24-hour link, and Preview 24-hour link.
  3. Click Share 24-hour link to copy a link that is valid for 24 hours (the recipient must download the file within this time), or Share internal link for a permanent link (only accessible to users with HubSpot access).
  4. Paste the link into your email body, e.g. "See service photos here" with a clickable link.
  5. Compose a new email from the contact record and send – the red error banner should no longer appear.

Option 2 – Compress images before attaching (if total size can be brought under 20 MB)

Use one of these free methods to reduce image size:

  • Via Paint (built into Windows): Right-click the image → Open with → Paint → File → Save as → choose JPEG. You can also resize the image under Home → Resize before saving.
  • Via the Photos app (built into Windows): Open the image in the Photos app → click the three dots (…) → Resize → choose a smaller size and save.
  • Via a free web tool: Go to squoosh.app or ilovepdf.com/compress-jpg, upload your images, choose the compression level, and download the compressed versions. Squoosh is especially handy as it shows the before/after file size in real time.

Option 3 – Zip files together (only if total zip size is under 20 MB)

If your files can be compressed to under 20 MB (under 4 MB for Outlook), you can zip them:

  1. Hold Ctrl and click to select all the files you want to send.
  2. Right-click on one of the selected files.
  3. Select "Compress to ZIP file" (Windows 11) or "Send to" → "Compressed (zipped) folder" (Windows 10).
  4. Right-click the newly created .zip file → Properties to check the total size.
  5. If the zip file is under 20 MB, attach it to the email. If it is still too large, use Option 1 (file links) instead.
  6. Compose a new email from the contact record, attach the zip file, and send.

Option 4 – Send directly from Outlook and add a note in HubSpot

If you need to send a large number of photos as real attachments, bypass HubSpot's sending limits entirely by composing the email in Outlook directly, then document it in HubSpot so the ticket stays up to date.

  1. Compose a new email in Outlook (not from HubSpot).
  2. Attach your images or files as normal. The sending limit is whatever your Office 365 tenant allows (typically 25–35 MB).
  3. Send the email — the customer will receive it as normal.
  4. Go back to the relevant ticket or contact record in HubSpot.
  5. Leave an internal note such as: "Email sent directly from Outlook due to large image attachments — customer has received it."

This keeps the ticket documented and makes it clear to any colleague viewing the record that the customer has been taken care of, even though HubSpot shows a failed send in the timeline.

Quick Reference – Size Limits

  • HubSpot one-to-one sales email: Max 20 MB total (attachments + inline images)
  • Connected Outlook / Office 365 inbox (via HubSpot): Max 4 MB total (email body + attachments + inline images)
  • Sent directly from Outlook + BCC logged to HubSpot: Up to 25–35 MB to send (Office 365 tenant limit), up to 40 MB for HubSpot to log
  • HubSpot BCC address: 8842163@bcc.hubspot.com

💡 Tip

Whenever you see "This email wasn't sent", always check the total attachment/image size first. If the size is within limits and the email still fails, contact Kajsa.