Why can't I send short messages with 139 mailbox now? Always prompt that the recipient cannot be empty? It's clearly filled out

How did you land? Mobile phone login directly 139 email interface or computer login? If you log in by mobile phone, you can try to change the access point, such as using CMWAP access point and CMNET access point respectively. The WAP page of 139 mailbox must use CMWAP mode. Or try a different browser like UCWEB. If the computer directly logs into the email address of 139, is the other party a normal user? In other words, the other party must have a normal mobile phone number, and ensure that the other party's sms channel is not blocked (that is, the other party's number is not blacklisted because it is sent too frequently).