我有安装ubuntu 15.4的实时服务器。我正在使用PHP。为此，我正在使用LAMP。在防火墙系统中，ufw就在那里。
我正面临着问题：我通过gmail电子邮件从我的服务器发送的图像（网络， 移动应用程序）它坏了（404错误）。但是在thunderbird，mac，还有 在雅虎，它显示正确。
我尝试使用另一台服务器，从该服务器发送电子邮件，它将正确显示在Gmail中。
我尝试了谷歌的每一个解决方案，但我无法弄清楚我的问题。我正在寻找这个过去6天。
我遇到同样的问题并尝试了所有建议Gmail's new image caching is breaking image links in newsletter
我已经提到谷歌的所有论坛。我的疑问是，这可能是因为我的服务器限制，但我无法弄清楚。禁用防火墙后我也试过了。但仍然没有。
我可以在2015年12月13日之前查看gmail电子邮件中的图片，之后它就会停止显示。 12月15日，我再次能够查看图像。但之后就停止了，目前它还没有显示出来。
我也尝试过不同的权限，用户和群组。
我的/ etc / default / ufw设置是
# Set to yes to apply rules to support IPv6 (no means only IPv6 on loopback
# accepted). You will need to 'disable' and then 'enable' the firewall for
# the changes to take affect.
IPV6=yes
# Set the default input policy to ACCEPT, DROP, or REJECT. Please note that if
# you change this you will most likely want to adjust your rules.
DEFAULT_INPUT_POLICY="DROP"
# Set the default output policy to ACCEPT, DROP, or REJECT. Please note that if
# you change this you will most likely want to adjust your rules.
DEFAULT_OUTPUT_POLICY="ACCEPT"
# Set the default forward policy to ACCEPT, DROP or REJECT. Please note that
# if you change this you will most likely want to adjust your rules
DEFAULT_FORWARD_POLICY="ACCEPT"
# Set the default application policy to ACCEPT, DROP, REJECT or SKIP. Please
# note that setting this to ACCEPT may be a security risk. See 'man ufw' for
# details
DEFAULT_APPLICATION_POLICY="SKIP"
# By default, ufw only touches its own chains. Set this to 'yes' to have ufw
# manage the built-in chains too. Warning: setting this to 'yes' will break
# non-ufw managed firewall rules
MANAGE_BUILTINS=no
#
# IPT backend
#
# only enable if using iptables backend
IPT_SYSCTL=/etc/ufw/sysctl.conf
# Extra connection tracking modules to load. Complete list can be found in
# net/netfilter/Kconfig of your kernel source. Some common modules:
# nf_conntrack_irc, nf_nat_irc: DCC (Direct Client to Client) support
# nf_conntrack_netbios_ns: NetBIOS (samba) client support
# nf_conntrack_pptp, nf_nat_pptp: PPTP over stateful firewall/NAT
# nf_conntrack_ftp, nf_nat_ftp: active FTP support
# nf_conntrack_tftp, nf_nat_tftp: TFTP support (server side)
IPT_MODULES="nf_conntrack_ftp nf_nat_ftp nf_conntrack_netbios_ns"
sudo ufw状态的输出是：
$ sudo ufw status
Status: active
To Action From
-- ------ ----
22 ALLOW Anywhere
22/tcp ALLOW Anywhere
80 ALLOW Anywhere
Apache ALLOW Anywhere
1433 ALLOW Anywhere
3306/tcp ALLOW Anywhere
80/tcp ALLOW Anywhere
25/tcp ALLOW Anywhere
22 (v6) ALLOW Anywhere (v6)
22/tcp (v6) ALLOW Anywhere (v6)
80 (v6) ALLOW Anywhere (v6)
Apache (v6) ALLOW Anywhere (v6)
1433 (v6) ALLOW Anywhere (v6)
3306/tcp (v6) ALLOW Anywhere (v6)
80/tcp (v6) ALLOW Anywhere (v6)
25/tcp (v6) ALLOW Anywhere (v6)
3306/tcp ALLOW OUT Anywhere
3306/tcp (v6) ALLOW OUT Anywhere (v6)
我正在使用SMTP。
我的服务器设置所需的任何其他信息都让我知道。
感谢。