Please select your desired mailbox here. Letterbox boxes are technically based on the 01 mailbox, and available in 3 fixed sizes (A4/A5/A6). Do you want a slightly different size? That's what BOXID is really good at!  
Choose the 01 Postal Box and enter your desired sizes and create boxes in any size you want. 
Should the contents be heavier than 2.5 Kg then our 01 Mailbox HD (heavy duty, from 2.5kg) will fit that.