Emails - Blocking

In this article you will learn:

• Under what circumstances email blocking occurs
• How to resolve blocking:
  • email sending
  • email receiving
• Frequently asked questions

---

Email blocking

By email blocking, we usually mean a situation where a mail server refuses to send or receive an email for some reason. Another common issue is the domain's DNS records setup, which may appear as email blocking upon receiving.

Email blocking may occur:

• Before sending an email, for example by blocking SMTP or the PHP mail() function on webhosting. You resolve the issue with the email service provider.
• Before receiving an email, for example due to routing failure or message rejection. The problem may be on the recipient's or sender's side.

---

Sending blocking

If sending mail is blocked on Mailhosting, Webhosting, WMS or WebSite, the system will not allow you to send any message. The mail client usually returns an error message, scripts fail.

Common reasons for blocking email sending include:

• Exceeding the daily quota for example when sending bulk mail or due to incorrect client configuration
• Preventive blocking due to suspicious behavior
• Full mailbox including the trash and SPAM folder
• Other reason

Daily quota

From webhosting services, you can send emails in two ways – via the SMTP mail protocol, or by the PHP mail() function. Each method has its own quota for sending emails (usually 500 emails per day, 50 for webhosting with the LowCost tariff).

If you exceed the quota, the system will block sending mail by that method until midnight, when the quota is reset.

Preventive blocking

If we detect problematic behavior in email accounts or entire services hosted by us, we block it to prevent damage and negative spam ratings of our email servers from spreading. Similar to the daily quota, we distinguish between sending mail via SMTP and the PHP mail() function.

Common reasons for blocking mail from our side include: 

• sending spam from an unsecured form or a compromised mailbox
• violation of the terms for sending emails

If we block your mail, a technician will send the service subscriber an email with instructions on how to resolve the issue. Take the recommended measures and then reply to the technician's message asking for the block to be removed.

Full mailbox

If the mailbox is full, it still sends emails, but it does not save them to Sent Mail or Drafts. 

You can resolve the situation by increasing mailbox capacity according to the guide E-mails – Increasing mailbox storage, or by deleting emails according to the guide WebMail – Deleting emails.

Other sending blocking on the server

If you suspect that the server is not sending emails, even though the service is not limited, ask support to check it via the form ⧉. Provide:

• the method of sending emails (SMTP via a mail client or script, PHP mail)
• the most accurate date and time the test message was sent
• the sender's email address
• the recipient's email address
• the full text or screenshot of any error message

---

Receiving blocking

If the recipient's server blocks the message, the sender will usually receive a non-delivery message describing the reason for rejection. Based on this message (or based on the fact that you do not receive anything at all), you can most easily determine whether delivery failed due to rejection by the server or due to another error.

Common reasons for blocking email reception include:

• Problems with SPF and DKIM, i.e. mechanisms that prevent spam sending
• The recipient's mailbox is full
• The sender or their server is on a blacklist
• Missing PHP mail() configuration, specifically the return-path reply address

Problem with SPF and DKIM

Problems with SPF and DKIM can either cause messages to end up in spam (in which case the recipient's server does not send a non-delivery message), or cause them to be rejected and the sender to be informed.

SPF is a TXT-type DNS record containing a list of servers that are authorized to send emails from addresses on this domain. More information and instructions for setting up an SPF record can be found in the article E-mails – SPF record, or from your email provider.

The error message for incorrect SPF settings varies depending on the recipient; VEDOS sends the following error:

550 5.7.1 <adresa@prijemce.tld>: Recipient address rejected: Please see http://www.openspf.net/Why?s=... (in reply to RCPT TO command)

For correct DKIM setup, verify that you have these records in DNS:

Název                       Typ     Data
key1.wedos-dkim._domainkey  CNAME   key1.dkim-we.wedos.net
key2.wedos-dkim._domainkey  CNAME   key2.dkim-we.wedos.net

For domains directed to Webhosting, WMS, or WebSite, the system generates these records automatically.

Full mailbox

If the mailbox is full, it cannot receive any more emails. 

You can resolve the situation by increasing mailbox capacity according to the guide E-mails – Increasing mailbox storage, or by deleting emails according to the guide WebMail – Deleting emails.

Blacklisting

The server may reject a message based on a blacklist, where it finds either an email address (a specific mailbox or the entire domain) or the IP address of the mail server.

There are many blacklists. One of them can be configured directly by the user, for example according to the article E-mails – Blacklist and whitelist in the customer administration. From the server on which your address is blacklisted in this way, a message will be returned to you after some time:

550 5.7.1 <adresa@prijemce.tld>: Recipient address rejected: sender blacklisted

Other blacklists are public or internal, and to remove an address from a blacklist you must contact the operator of the sender's mail servers. If you are sending an email from our Webhosting, WMS, or WebSite, and you receive a non-delivery message mentioning the IP address of the mail server being placed on a blacklist, send us the error message wording via the form ⧉. A technician will handle the next steps.

PHP mail() and return-path

If your emails sent via the PHP mail() function are not being delivered, check that the return-path parameter is filled in correctly according to the pattern:

mail('adresa@prijemce.tld','Předmět','Text zprávy','','-f adresa@odesilatele.tld');

Avoid setting return-path to the address entered by the user in the form, and instead use an address on the domain from which you are sending the email.

Other receiving blocking on the server

If you suspect that the server is not receiving emails even though the sender's domain has at least the SPF record set correctly and there is enough free space in the mailbox, ask support to check it via the form. Provide:

• the most accurate date and time the test message was sent
• the sender's email address
• the recipient's email address
• the full text or screenshot of any error message

---

Frequently asked questions