The limit is on the whole message
Attachment caps apply to the total message, not to each file, and attachments are encoded for transport in a way that inflates them by roughly a third. A message of files totalling twenty megabytes therefore arrives at the limit sooner than the arithmetic suggests. Budget for that rather than sending right up to the stated figure.
The receiving server has its own limit too, and it may be lower than your provider allows you to send. A message accepted at your end can still bounce at theirs.
Compress the batch, not one file
Where email attachments are concerned, the useful operation is on the set. Drop all the pictures in together, give them a shared target, and the total falls predictably. Compressing one at a time and checking the running total by hand is the slow way to the same place.
JPEG is the right format here because it opens everywhere, including in older desktop mail clients that may not display WebP.
When to use a link instead
If the recipient needs the originals — for printing, editing or archiving — do not compress them at all. Share them through a link and send the untouched files, because compression for transmission is not something they can undo at the other end.
Questions
- Why did my email bounce even though the attachments were under the limit?
- Attachments are encoded for transport, which adds roughly a third to their size, so the message is larger than the sum of the files. The recipient server may also enforce a lower limit than your provider. Aim for comfortably under the stated cap rather than just beneath it.
- What is a safe total size for photo attachments?
- Keeping the whole message under about ten megabytes is safe with nearly every provider and corporate mail server. For ten photographs that works out to a few hundred kilobytes each, which is comfortable for pictures that will be viewed on a screen rather than printed.
- Will the recipient notice the compression?
- For pictures viewed on a screen at normal size, almost never. Use the comparison slider before attaching and judge for yourself. If the recipient will print them or edit them, send the originals through a share link instead, because what compression removes cannot be restored later.
- Should I put the pictures in a zip archive instead?
- A zip keeps a set tidy and arrives as one item, which some recipients prefer. What it will not do is make photographs meaningfully smaller — they are already compressed, and general purpose archiving finds almost nothing further to remove. Reduce the pictures first, then archive them if grouping is what you actually want.