Having issues connecting to a SMTP server with curl. The script I am running has worked on other hosts so its an issue with curl. Ubuntu version 16.04 (xenial). The pre installed curl version was 7.47. Everytime I run a command similar to this curl --url \'smtps://smtp.gmail.com:465\' ...the rest of the args I get the error

curl: (1) Protocol "'smtps" not supported or disabled in libcurl

Very strange since I've had previous ubuntu installations that came with curl pre installed and had smtp support.

curl --version

outputs this

curl 7.47.0 (x86_64-pc-linux-gnu) libcurl/7.47.0 GnuTLS/3.4.10 zlib/1.2.8 libidn/1.32 librtmp/2.3 Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3 pop3s rtmp rtsp smb smbs smtp smtps telnet tftp Features: AsynchDNS IDN IPv6 Largefile GSS-API Kerberos SPNEGO NTLM NTLM_WB SSL libz TLS-SRP UnixSockets

as you can see smtp and smtps are listed as protocols but i am unsure whether they are the ones enabled or supported?

Heres what I've done following the advice of similar threads

uninstalled curl with sudo apt-get remove curl then followed the answer here

whenever it was time to run the configure script i gave it the following options

./configure --with-ssl --enable-smtp --enable-smtps

after i finished, i got the same error... Then i tried reinstalling with apt-get install curl. but still get the same error. What gives? if there are no ways to resolve this gracefully, could I accomplish the same thing with wget?

  • I just tested your start with my account and I got the same error with the \' on the smtps part. If I removed those it worked fine. Leaving the ' or no quotes there didn't matter and it worked fine either way.
    – Terrance
    Oct 1, 2018 at 23:10

1 Answer 1


You have a leading apostrophe (') since you're escaping it with a backslash (\) - The output is a bit hard to read but curl is trying to tell you this, but since it's next to some double quotes (") it doesn't stand out:

curl: (1) Protocol "'smtps" not supported or disabled in libcurl
  • holy cow you are 100% correct, I was copying and pasting the test command and I didnt realize the ' was still in there. Everything worked and I just threw away a few hours of my life haha. Thanks for pointing that out.
    – Alan
    Oct 2, 2018 at 0:24

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