Best Image Formats for Email and Messaging Apps

Attachment limits stated by the providers

These figures come from each provider's own help pages as checked on 6 November 2026. Limits change, and organizations running their own mail systems can set different ones, so treat the table as a starting point.

Service	Stated limit	What the provider says
Gmail (personal)	25 MB	Above the limit, the attachment becomes a Google Drive link
Google Workspace (work, school)	Set by the administrator	Varies by organization
Outlook.com and other internet accounts in Outlook	20 MB	Counts the attachment and the message together
Exchange (business) in Outlook	10 MB default	Stated as the default; administrators can differ
iCloud Mail	20 MB, up to 5 GB with Mail Drop	Applies to incoming and outgoing messages

Why 15 MB of photos can still be refused

Email was designed for text. Binary attachments are converted to text characters before sending, usually with Base64, which turns every 3 bytes into 4 characters, and the message is split into lines of about 76 characters. Together this adds roughly 37 percent to the size on the wire. Whether a provider counts the encoded or the original size varies, and Microsoft's page states that its limit includes the attachment and the message together, so plan with a margin.

Here is the arithmetic with a made-up set of files. Four photos of 4 MB each total 16 MB. Encoded, that is about 16 x 1.37 = 21.9 MB. That could pass a 25 MB limit but fail a 20 MB one, even though 16 is less than 20. The same four photos reduced to 1 MB each would total about 5.5 MB encoded and pass anywhere.

Scenario: a handful of photos to family or friends

Send: JPEG, longest side 1600 or 1920 pixels. A phone photo of 4032 by 3024 pixels has 12.2 megapixels; at 1600 by 1200 it has 1.92, so about 6.4 times fewer pixels, and on a phone or laptop screen the smaller picture looks almost identical because the screen cannot show more detail than that. The file will usually be several times smaller too, not in exact proportion.

Avoid: sending HEIC straight from an iPhone to people whose device you do not know. Android decodes HEIF only from version 9 and only where the device supports it, and Windows usually needs an extension. Converting first removes the question; the HEIC and JPEG comparison explains why. Apple devices sometimes convert photos for you when you share, but you cannot count on that for every method.

Resizing inside the mail program may not shrink the file

Microsoft's support page on reducing attachment size notes that in the new Outlook for Windows, changing the size of an inserted picture changes how large it appears in the message and does not reduce its file size. That is easy to misread: the picture on screen looks smaller, yet the attachment is still the original weight and counts fully against the limit. If the goal is to get under a size limit, resize and re-save the picture before inserting it.

For the same reason, always check the file size shown in the folder or on the converter's result row, not the size you see on screen.

Scenario: a screenshot for support or a colleague

Send: PNG. Screenshots are flat areas and text, which PNG stores exactly and often at a small size; JPEG would add faint speckles around letters. In the synthetic 1920 by 1080 interface-style test described in the website format guide, PNG was 119,602 bytes against 263,809 for JPEG at quality 90.

Avoid: BMP. A 24-bit BMP stores every pixel without compression, so a 1920 by 1080 screenshot is 6,220,800 bytes of pixel data before any file header, which is more than 6 MB for a picture that PNG holds in a small fraction of that.

Watch out for: screenshots of sensitive screens. Cropping is not available in this converter, so do it in the screenshot tool or an editor before sending.

Scenario: sending a photo through a chat app

Chat apps usually re-encode photos you send as pictures, reducing both dimensions and quality to save bandwidth. Several also let you send the same file as a document or file, which skips that step. Where the setting lives and what it is called differs by app and version, and some apps expose an upload-quality preference in their storage or data settings, so check your app rather than assuming.

The practical consequence is double compression: your JPEG goes through the app's encoder, and if the receiver forwards it, through another one. Each pass is lossy. Start from a clean, moderately sized JPEG and the extra passes do little visible harm; start from an already heavily compressed small file and you will see blocks and smeared detail. The quality guide shows how those losses accumulate.

Formats to avoid in messages, and one exception

• HEIC: unreadable for some recipients and for many web mail previews.
• BMP and TIFF: huge for what they contain; many mail clients show them poorly or not at all.
• WebP and AVIF: fine in current browsers, but older mail programs and some corporate tools may not show them inline. If you are not sure, JPEG or PNG is safer.
• Animated GIF: works in most places but is large for the motion it carries; and if you convert one with this tool, you get its first frame only.

The exception is when the recipient asked for a specific format. Follow the request, even if it is not the one you would choose. Some organizations, for example, ask for scans as JPEG or PDF only, and an attachment in any other format simply gets bounced by their mail filter, which costs a day.

Links instead of attachments, and documents

When a set of photos will not fit however you shrink them, a link is the better route. Gmail does this itself above its limit, replacing the attachment with a Google Drive link, and Apple's Mail Drop raises the iCloud Mail ceiling to 5 GB by delivering large files as a download. Both depend on the recipient being able to open the link, which is worth confirming for company mail systems that block them.

Multi-page material is different. A scan of a contract or a form with several pages is best sent as one PDF, not as several images, and this converter cannot create PDF files, so use the scanning app or print-to-PDF function for that. For a single page, a JPEG of about 2000 pixels or more on the long side (roughly 170 ppi on an A4 page) is readable on a screen; text-heavy pages in PNG stay crisper but are larger.