In short: not in practice. Emails sent to Info@Pelda.hu, info@pelda.hu and INFO@PELDA.HU arrive in the same inbox in the email systems used today. The standard is more nuanced than this, so it is worth knowing why things work this way and what you really need to bear in mind when entering an address.

The two parts of the address

An email address consists of the local part (the part before the @ symbol, for example info) and the domain (the part after the @ symbol, for example pelda.hu). Different rules apply to each of these two parts.

• Domain names are not case-sensitive, because according to DNS rules, Pelda.HU and pelda.hu are the same name. This is the case in all email systems, without exception.
• The local part may, in theory, be sensitive according to the SMTP standard (RFC 5321): the standard stipulates that servers relaying the message must preserve the case of the letters, and the recipient’s server may decide that Anna and anna are two separate mailboxes. However, the same standard expressly advises against anyone exploiting this, as it only causes confusion.

What happens in practice?

The mail servers of major email service providers and web hosting providers treat the local part of the address as case-insensitive, so no emails are lost due to differences in letter case. Mailboxes created on the email hosting service work in the same way: if a contact enters their address in upper case, the email will still be delivered.

What really matters, however, is:

• Typing error: a single transposed or missing letter (e.g. ifno@) or an incorrect extension (e.g. pelda.com instead of pelda.hu) results in a different or non-existent address. In such cases, the email bounces back or, in the worst case, ends up in someone else’s inbox.
• Full stops and plus signs: some providers, such as Gmail, ignore full stops in usernames and deliver addresses in the format nev+valami@ to the nev@ mailbox. This is a provider-specific feature, not a general rule, so it is not advisable to rely on it with other systems.
• Addresses with diacritics: the local part of the address containing diacritics (for example, józsef@) is now standard, but not all mail servers and programs support it; we therefore recommend using a version without diacritics for business addresses.

Recommended practice

1. Always write your company name in lower case, and use this form on your business cards, website and in your signature. The lower-case form is the most legible and does not bother anyone.
2. When storing and comparing addresses on website forms, in online shops or on newsletter lists, ensure they are in lower case; otherwise, the same customer may end up with two separate accounts or two subscriptions.
3. If you receive an address that has been dictated or written by hand, please check it letter by letter, paying particular attention to the domain extension.
4. If an email bounces back with an error such as ‘user unknown’ or similar, first check the spelling of the address and the domain. The error messages for bounced emails are explained in our article on 550 email errors.

In summary

Capital letters do not prevent delivery, but typos do. If you enter the address exactly as it is, in lower case, you will never have any problems due to the case of the letters.