Apple's iPhone smartphone device lets users download files sent to them as attachments in email messages and attach and send files to their contacts using the "Mail" application. The size of the files that can be uploaded and downloaded as attachments is not limitless, however. On the iPhone, the maximum size of the attachments that you can download and upload is based on two things: the attachment limit on the iPhone device and the attachment limit set by your email provider.
iPhone Attachment Upload Limit
The iPhone does not have a file size limit for the files that you want to upload and send as attachments. The device does limit the types of files that you can send, however. Since the iPhone does not have a disk mode, only applications that have email support can attach files to emails. By default, the only application that has the ability to attach photos and videos to an email message is the "Photos" application.
iPhone Attachment Download Limit
The iPhone also does not have a file size limit for the files that you want to download from emails. The only limit in place is the size of your iPhone's hard drive. If there is no available space left on your device, you will be unable to download the attachment.
Email Provider Attachment Limit
While the iPhone may not have any attachment download and upload limits, the email account that you have synced with your iPhone might. This type of attachment download and upload limit is imposed by your email provider and applies to any and all devices that make use of the provider's email service. For example, Gmail, Yahoo! Mail and Windows Live Mail all have attachment limits of 25MB, so you will be unable to upload or download any file that exceeds this size.
Contact's Email Provider Attachment Limit
When sending a file as an attachment from your iPhone, you must also take the contact's email provider's attachment limit into account. If you attempt to send a file that is larger than the contact's email provider's attachment limit, the attachment will not go through, regardless of your email provider's attachment limit.