First of all, this is not the issue from the Sharetronix software so it couldn't considered as bug.( May u have posted in wrong section. But no issues)
Message delivery is purely depends on the trust factors of website it have, so if your web hosting company has assigned a white-listed ip then there is lot of possibilities there to deliver the mails in the inbox. In the opposite side if your web hosting company assigned the IP that was blacklisted with SPAM watch sites then there are lot of opportunities that your mails wont' delivered in inbox.
To resolve this issue you have two choices
Ask your web hosting company to assign a white list IP( Most of shared hosting company can do this for paying some extra dollar every month, if you are using VPS or Dedicated plan you may get it free)
If the first plan wouldn't work then you may use SMTP mailing instead of default mail functions used by sharetronix. You can get the SMTP mail extension from our below Community page
http://sharetronixguide.com/topic/11/sm
om-marbed/
Create a email account and provide the login credentials with the SMTP mailer and upload it. Now onwards the mail from your sharetronix website will be sent through SMTP mailing .
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