SMTP (Send/simple mail transfer protocol) servers are servers used to send your emails through.

An ISP generally does not allow you to send emails through it (relay) unlesss you are connected through them directly. Some ISPs however do allow you to send mails in this case if you authenticate yourself before sending mails.

SMTP servers mostly work on port 25 and some allow port 587 as a secondary option. When travelling and using WiFi hotspots or hotel internet access you may find errors in sending emails (this occurs with using iBurst too). In these cases, try and switch your authenticate before sending or changing the ports. This 'error' occurs as the place providin you internet access is trying to relay your emails and send them and not allow you to access your designated ISP.

•  Firewater : smtp.fwinternet.net
•  Firewater / 1and1 : auth.1and1.co.uk
•  Telkom ADSL : smtp.dsl.telkomsa.net or smtp.saix.net
•  Telkom Analogue Dial Up, use smtp.saix.net or smtp.dsl.telkomsa.net
•  8TA (Eita), the outgoing server is smtp.saix.net 
•  MWEB ADSL : smtp.mweb.co.za or smtp.mweb.net
•  Vodacom 3G : smtp.vodacom.co.za
•  MTN 3G, the outgoing server is mail.mtn.co.za
•  Cell C the outgoing server is mail.cmobile.co.za
•  Iburst : smtp.iburst.co.za
•  I.S. ADSL the outgoing server is smtp.isdsl.net
•  I.S. 3G the outgoing server is smtp.isgsm.netor smtp.dial-up.net
•  goggaconnect outgoing server is smtp.vodacom.co.za
•  Neotel : smtp.neomail.co.za
•  ABSA : smtp.absamail.co.za or mail.absa.co.za 
•  @lantic (ADSL,Dialup, ISDN) : smtp.lantic.net
•  NetActive (ADSL,Dialup, ISDN) : smtp.netactive.co.za
•  Polka (ADSL,Dialup, ISDN) : smtp.polka.co.za
•  Web Africa (ADSL,Dialup, ISDN) : smtp.wa.co.za