Hey maurizio284,
If iCloud Photos is enabled, this would be expected behavior from iOS. YOu'll share a link to iCloud that can be accessed for up to 30 days, during which recipients can download the full-res images to their devices.
See more info here: Share photos and videos on iPhone - Apple Support
"Share photos and videos
- Share a single photo or video: Open the photo or video, tap , then choose a share option.
- Share multiple photos or videos: When viewing a screen with multiple thumbnails, tap Select, then tap the thumbnail of the photos and videos you want to share. Tap , then choose a share option.
- Share photos or videos from a day or month: Tap Library, tap Days or Months, tap , then tap Share Photos and choose a share option.
When iCloud Photos is turned on, you can share multiple full-quality photos with an iCloud link. iCloud links remain available for 30 days, can be viewed by anyone, and can be shared using any app, such as Messages or Mail.
You can also use Shared Albums to share photos and videos with just the people you choose. See Use iCloud Shared Albums with iPhone.
Note: The size limit of attachments is determined by your service provider. For devices or services that don’t support Live Photos, a Live Photo is shared as a still photo."
Cheers!