Attachment cannot be opened or sent: the solutions

The document you can’t open, the photo arriving as a « file.dat », the rejected send due to « attachment too large », the zip blocked « for your security » : the attachment is the oldest email service and the most accident-prone. Each blockage, however, has a specific cause — the unknown format, the size, the security filter, the missing app — and a solution in two minutes. The guide to all stubborn attachments, both for sending and receiving — and the real rules of caution, as some blockages are there to protect you.

« I can’t open it » : the format problem

The file arrives but nothing opens it — three cases : the format without an application — the file extension (.pages, .odt, .heic, .dwg…) indicates which tool it expects : the solution is NOT to force (the stubborn double-click) but to identify — search « open file [extension] » : the free viewer almost always exists, and especially CONVERSION works better (ask the sender for a PDF — the universal format that opens everywhere : the real answer to 80 % of format issues is « resend it as a PDF », and our word processing guides teach exporting in three clicks — pass the tip to the repeat offender sender) ; the file « .dat » or without a name — the attachment mutilated in transit (the classic « winmail.dat » from old corporate email systems : the file is inside, free tools extract it — but the simplest solution is to have it resent « as a normal attachment ») ; and the truly corrupted file — the interrupted transfer (the PDF that opens halfway, the truncated image) : have it resent, and if ALL sends from this person arrive broken, the problem is on their end (their email app, their connection). The test that always distinguishes : the same file from the webmail (the browser) rather than the app — webmail downloads raw : if it opens there, it’s your email app that’s mutilating it ; if it’s broken everywhere, it’s the file.

« Too large » : the size, and the real solution

The most frequent send refusal — and the best resolved : email boxes cap attachments (typically 20-25 Mo — and the recipient has THEIR limits : the sent email may be refused upon arrival) : when faced with refusal, three levels : the auxiliary compression — photos shrink upon sending (the « message size » options in email apps — the 8 Mo photo becomes 800 Ko without visible loss on screen : enough to show, insufficient to print — choose according to usage), PDFs compress (built-in and online tools — caution with sensitive documents in online compressors : see the box), the entire folder zips (right-click → compress) ; the sharing link — THE real modern solution beyond a few megabytes : the file uploaded to your cloud space, the LINK sent by email (our sharing guides — the recipient downloads in one click, no inbox fills up, very large files pass, and the link can be revoked) : webmails even suggest it automatically beyond the threshold — accept their suggestion ; and the temporary sending services for occasional large files (large file sending platforms — free for regular use, the link expires on its own) : practical for a recipient without an ecosystem. The golden rule that simplifies everything : under 5 Mo — attachment ; beyond — link : your sends will always go through, and your inboxes (our full inbox guides) will thank you.

The right reflex. For phone photos that « won’t send » : the modern culprit is often the HEIC format (the efficient format of iPhones, which some old Windows recipients can’t open) : the « Most compatible » setting (Settings → Camera → Formats) takes photos in universal JPEG, and sharing via email automatically converts in most cases — but if a recipient complains about unreadable photos, you now know what to answer : « I’ll resend them in JPEG » (sharing via the conversion option, or a screenshot as a quick fix).

« Blocked for your security » : the filters, and why they’re often right

The email refuses certain files BY PRINCIPLE — understanding protects : the banned types — executable files (.exe, .bat, .js and the like) are refused by all major email services, even zipped (this is THE historical vehicle of viruses — and this blockage cannot be bypassed : it MUST NOT — legitimate software is transmitted via a link to its official source, never as an attachment) ; the encrypted and suspicious zips — the password-protected zip raises filters (malware hides from the scanner) : legitimate use exists (the confidential document — see the box for better), but expect friction ; the macros — the Office document « with active content » triggers warnings and quarantines : upon receipt, the absolute rule — macros from a received document are NEVER ACTIVATED (the yellow « enable content » button is the number one trigger of ransomware — our guides : no legitimate document in everyday life requires macros) ; and the corporate quarantines — professional email filters harder (the « held » attachment is released via the IT service, not via a bypass). The right reflex on both sides : when SENDING an unusual file, warn and prefer the link ; when RECEIVING a blockage, first ask if the filter isn’t right — the « invoice.zip » unexpectedly blocked by your email service is a favor, not a failure (our phishing guides : the sender is verified before the file).

Everyday cases, resolved one by one

The collection of real-life situations : the PDF that asks for a password — protected by the sender (pay slips, statements : the password is agreed upon or indicated — often a combination of your birth date : reread the accompanying email) ; the invisible attachment — the paperclip without a file : the image embedded IN the email body (right-click on the image → save), or the forwarded email that lost its attachments (the « online » vs « as attachment » transfer — have the original resent) ; the download that fails repeatedly — full disk space (our guides), unstable network (try again on stable Wi-Fi), or antivirus intercepting (its quarantine will say) ; the preview that betrays — the document that displays oddly IN the email but perfectly once downloaded and opened in its real app (the email preview is basic : download before judging — and before printing : printing from the preview makes broken layouts) ; the phone scan too heavy — the scan quality setting (our digitization guides : the 40 Mo PDF for three pages signals excessive resolution) ; and the self-send that doesn’t go through — the stuck outbox (the email app offline, the giant draft stuck in the queue : delete the stuck message from the outbox, the queue resumes — THE remedy for « my emails haven’t been sending since yesterday »).

Frequent questions

Why do my photos arrive blurry/degraded with some recipients ?

Compression along the way : your app sent in « reduced size » (the choice at sending — take « actual size » for printing), or the recipient’s email service compresses. For photos that matter (prints, memories) : the sharing link transmits the original intact — it’s even its domain (our shared photos guides).

Can I send an entire folder by email ?

Not as is — email only takes files : the folder is zipped (right-click → compress : a single clean file) if it’s light, or shared as a cloud folder link if it’s heavy or evolving (the link always shows the latest version — the decisive advantage over the frozen zip).

The recipient says they received nothing, but my email is well « sent » :

The trio of verification : their spam folder (the attachment makes it classified as unwanted — especially zips), the size (their server may have refused — the non-delivery error message sometimes arrives hours later, look for it), and the exact address (the silent typo). Resending as a sharing link bypasses all three at once — and confirms the correct address via an additional channel in the process.

What to remember

The blocked attachment always has a clear cause : the format (the missing viewer — and the PDF as a universal answer : have it resent, or convert), the size (auxiliary compression under 5 Mo, LINK for sharing beyond — the golden rule that resolves sending, receiving, and your quotas), the security (banned executables for good reason, macros never activated, quarantines that protect — some blockages are services), and the everyday classics (webmail as the judge, stuck outbox purged, HEIC converted, preview downloaded before printing). All under the constant vigilance : the unexpected is verified before opening — the attachment is the preferred entry point for attacks, and your caution is its best lock. The client’s document will be back in five minutes — as a link, and it can weigh 2 Go if it wants.